ebaz4205: Remove PS7 support for now (since untested and we'll avoid the .xci in LiteX-Boards repository).

Usage:

```
./ebaz4205.py --cpu-type=vexriscv --build --load
```

```
$ pwd
litex-boards/litex_boards/targets
```

Tip: Use `GTKTerm` to connect to /dev/ttyUSB0 (usually) and interact
with the LiteX BIOS.

References:

- https://github.com/fusesoc/blinky#ebaz4205-development-board
- https://github.com/olofk/serv/#ebaz4205-development-board
- https://github.com/xjtuecho/EBAZ4205#ebaz4205
- https://github.com/nmigen/nmigen-boards/pull/180 (merged)
- https://github.com/olofk/corescore/pull/33
- The existing 'Zybo Z7' example

Note: The `PS7` stuff remains untested via LiteX for now.

Leads to an increase in DP16KD, first noticed in
https://github.com/enjoy-digital/liteeth/issues/70.
With full_mem_we:
```
Info: 	              DP16KD:    41/   56    73%
```
Without:
```
Info: 	              DP16KD:    29/   56    51%
```

targets: Remove old call to add_spi_flash on targets now using LiteSPI (we'll find it with gitk is required).

Signed-off-by: Joey Bushagour <jbushagour@google.com>

This is now required since ECP5PLL now checks that PFD is in required range.

Keep the old add_spi_flash call commented for now just in case we need to compare/test it.

Already better regarding resource usage:
Info: 	         ICESTORM_LC:  2938/ 5280    55%
Info: 	        ICESTORM_RAM:     2/   30     6%
Info: 	               SB_IO:    15/   96    15%
Info: 	               SB_GB:     8/    8   100%
Info: 	        ICESTORM_PLL:     1/    1   100%
Info: 	         SB_WARMBOOT:     0/    1     0%
Info: 	        ICESTORM_DSP:     0/    8     0%
Info: 	      ICESTORM_HFOSC:     0/    1     0%
Info: 	      ICESTORM_LFOSC:     0/    1     0%
Info: 	              SB_I2C:     0/    2     0%
Info: 	              SB_SPI:     0/    2     0%
Info: 	              IO_I3C:     0/    2     0%
Info: 	         SB_LEDDA_IP:     0/    1     0%
Info: 	         SB_RGBA_DRV:     0/    1     0%
Info: 	      ICESTORM_SPRAM:     4/    4   100%

Requires https://github.com/enjoy-digital/litex/commit/80e9d2cea9198b38f62a68bc420328222b3b6709

Already better regarding resource usage:

Info: 	         ICESTORM_LC:  2358/ 5280    44%
Info: 	        ICESTORM_RAM:     2/   30     6%
Info: 	               SB_IO:    15/   96    15%
Info: 	               SB_GB:     8/    8   100%
Info: 	        ICESTORM_PLL:     1/    1   100%
Info: 	         SB_WARMBOOT:     0/    1     0%
Info: 	        ICESTORM_DSP:     0/    8     0%
Info: 	      ICESTORM_HFOSC:     0/    1     0%
Info: 	      ICESTORM_LFOSC:     0/    1     0%
Info: 	              SB_I2C:     0/    2     0%
Info: 	              SB_SPI:     0/    2     0%
Info: 	              IO_I3C:     0/    2     0%
Info: 	         SB_LEDDA_IP:     0/    1     0%
Info: 	         SB_RGBA_DRV:     0/    1     0%
Info: 	      ICESTORM_SPRAM:     4/    4   100%

We can still try to reduce it, but enabling Master should not use that much LCs.

Both XiP from SPI(1X) or QSPI(4X) are working, but resource usage is currently
too high to be able to switch to it by default. We'll first try to reduce it.

Resource usage using SPI(1X) and actual LiteX SPI Flash core:
Info: Device utilisation:
Info: 	         ICESTORM_LC:  2016/ 5280    38%
Info: 	        ICESTORM_RAM:     2/   30     6%
Info: 	               SB_IO:    15/   96    15%
Info: 	               SB_GB:     8/    8   100%
Info: 	        ICESTORM_PLL:     1/    1   100%
Info: 	         SB_WARMBOOT:     0/    1     0%
Info: 	        ICESTORM_DSP:     0/    8     0%
Info: 	      ICESTORM_HFOSC:     0/    1     0%
Info: 	      ICESTORM_LFOSC:     0/    1     0%
Info: 	              SB_I2C:     0/    2     0%
Info: 	              SB_SPI:     0/    2     0%
Info: 	              IO_I3C:     0/    2     0%
Info: 	         SB_LEDDA_IP:     0/    1     0%
Info: 	         SB_RGBA_DRV:     0/    1     0%
Info: 	      ICESTORM_SPRAM:     4/    4   100%


Resource usage using LiteSPI:
Info: Device utilisation:
Info: 	         ICESTORM_LC:  3964/ 5280    75%
Info: 	        ICESTORM_RAM:     2/   30     6%
Info: 	               SB_IO:    15/   96    15%
Info: 	               SB_GB:     8/    8   100%
Info: 	        ICESTORM_PLL:     1/    1   100%
Info: 	         SB_WARMBOOT:     0/    1     0%
Info: 	        ICESTORM_DSP:     0/    8     0%
Info: 	      ICESTORM_HFOSC:     0/    1     0%
Info: 	      ICESTORM_LFOSC:     0/    1     0%
Info: 	              SB_I2C:     0/    2     0%
Info: 	              SB_SPI:     0/    2     0%
Info: 	              IO_I3C:     0/    2     0%
Info: 	         SB_LEDDA_IP:     0/    1     0%
Info: 	         SB_RGBA_DRV:     0/    1     0%
Info: 	      ICESTORM_SPRAM:     4/    4   100%