With colorbars for now, need to free up BRAMS for Video Terminal (or finish HyperRAM support).

sipeed_tang_nano: Add SPI Flash, Enable CPU and use new external SPI Flash support from OpenFPGALoader.

./sipeed_tang_nano_4k.py --cpu-type=vexriscv --cpu-variant=lite --build --flash

        __   _ __      _  __
       / /  (_) /____ | |/_/
      / /__/ / __/ -_)>  <
     /____/_/\__/\__/_/|_|
   Build your hardware, easily!

 (c) Copyright 2012-2021 Enjoy-Digital
 (c) Copyright 2007-2015 M-Labs

 BIOS built on Sep 17 2021 15:54:08
 BIOS CRC passed (6cc6de6d)

 Migen git sha1: a5bc262
 LiteX git sha1: 46cd9c5a

--=============== SoC ==================--
CPU:		VexRiscv_Lite @ 27MHz
BUS:		WISHBONE 32-bit @ 4GiB
CSR:		32-bit data
ROM:		64KiB
SRAM:		8KiB
FLASH:		4096KiB

--========== Initialization ============--

Initializing W25Q32 SPI Flash @0x80000000...
SPI Flash clk configured to 13 MHz
Memspeed at 0x80000000 (Sequential, 4.0KiB)...
   Read speed: 1.3MiB/s
Memspeed at 0x80000000 (Random, 4.0KiB)...
   Read speed: 521.9KiB/s

--============== Boot ==================--
Booting from serial...
Press Q or ESC to abort boot completely.
sL5DdSMmkekro
Timeout
No boot medium found

--============= Console ================--

litex>

./sispeed_tang_nano_4k.py --build --load

Build with Gowin EDA.
Load with OpenFPGALoader.

Validated with:
./gsd_butterstick.py --uart-name=crossover --with-etherbone --csr-csv=csr.csv --build --load
litex_server --udp
litex_term bridge


        __   _ __      _  __
       / /  (_) /____ | |/_/
      / /__/ / __/ -_)>  <
     /____/_/\__/\__/_/|_|
   Build your hardware, easily!

 (c) Copyright 2012-2021 Enjoy-Digital
 (c) Copyright 2007-2015 M-Labs

 BIOS built on Sep  1 2021 19:09:52
 BIOS CRC passed (3d349845)

 Migen git sha1: 27dbf03
 LiteX git sha1: 315fbe18

--=============== SoC ==================--
CPU:		VexRiscv @ 75MHz
BUS:		WISHBONE 32-bit @ 4GiB
CSR:		32-bit data
ROM:		128KiB
SRAM:		8KiB
L2:		8KiB
SDRAM:		524288KiB 16-bit @ 300MT/s (CL-6 CWL-5)

--========== Initialization ============--
Initializing SDRAM @0x40000000...
Switching SDRAM to software control.
Read leveling:
  m0, b00: |01110000| delays: 02+-01
  m0, b01: |00000000| delays: -
  m0, b02: |00000000| delays: -
  m0, b03: |00000000| delays: -
  best: m0, b00 delays: 02+-01
  m1, b00: |01110000| delays: 02+-01
  m1, b01: |00000000| delays: -
  m1, b02: |00000000| delays: -
  m1, b03: |00000000| delays: -
  best: m1, b00 delays: 02+-01
Switching SDRAM to hardware control.
Memtest at 0x40000000 (2.0MiB)...
  Write: 0x40000000-0x40200000 2.0MiB
   Read: 0x40000000-0x40200000 2.0MiB
Memtest OK
Memspeed at 0x40000000 (Sequential, 2.0MiB)...
  Write speed: 13.6MiB/s
   Read speed: 15.6MiB/s

--============== Boot ==================--
Booting from serial...
Press Q or ESC to abort boot completely.
sL5DdSMmkekro
Timeout
No boot medium found

--============= Console ================--

litex>

- Now uses regular UART.
- Build tested with: ./quertyembedded_beaglewire.py --cpu-type=serv --build
- Can still be build with Crossover UART with --uart-name=crossover+bridge.

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.

**Problems**

`SPIMaster` pad names are `clk`, `cs_n`, `mosi`, and `miso`.
However, `feather_spi` is using `sck` instead of `clk`, therefore
it is not able to use as-is for `SPIMaster`, for example,
with `add_spi` on Linux On LiteX VexRiscv.

**Solution**

In fact, `spisdcard` and other SPI related pad names are
using `clk`, only `feather_spi` is using `sck`.
Therefore, rename `sck` to `clk`.

This board is documented as having the LIFCL-40-9BG400C part, but some
versions of the board exist which were fitted with LIFCL-40-8BG400CES,
an engineering sample part. The distinction is important because the
engineering sample requires a different device ID to be embedded in the
bitstream. If you try to build a bitstream for LIFCL-40-9BG400C and load
it onto LIFCL-40-8BG400CES the configuration fails (indicated by the red
"INITN" LED on this board).

Accept --device to allow the user to specify which FPGA part their board
has.