targets/acorn_cle_215: use new generate_litepcie_software functions and add --driver argument to generate driver.

targets/acorn_cle_215: automatically copy software from litepcie and generate headers in kernel directory.

ZCU104: add I2C

Tested with:
./pano_logic_g2.py --uart-name=jtag_uart --build --load
./litex_jtag_uart.py --config=openocd_xc6_ft232.cfg
lxterm /dev/pts/X

Take Ethernet PHY out of reset so default clock is 125 Mhz

Tested with:
./forest_kitten_33.py --uart-name=jtag_uart --build --load
litex/tools/litex_jtag_uart.py
lxterm /dev/pts/X

platforms/nexys4ddr: add option to build with spi-mode sdcard support

platforms/ecp5_evn: rename spiflash1x to spiflash, rewrite hardware/configuration description and remove make_spiflash.

The Platform file should not contain import code related to cores, this has to be done in the target.

ECP5-EVN SpiFlash parameters

[WIP] Add Alveo U250 platform and target