Lattice Crosslink-NX EVN support

[josuah]

This issue is there to allow to reproduce more easily the several recent merge requests associated with the support of that board:

• https://github.com/enjoy-digital/litex/pull/1747
• https://github.com/enjoy-digital/litex/pull/1748
• https://github.com/enjoy-digital/litex/pull/1749
• https://github.com/litex-hub/zephyr-on-litex-vexriscv/pull/17
• https://github.com/litex-hub/zephyr-on-litex-vexriscv/pull/19
• https://github.com/litex-hub/zephyr-on-litex-vexriscv/pull/13
• https://github.com/zephyrproject-rtos/zephyr/pull/61640

Once everything gets merged on LiteX-side, it would be a good time to remove the [draft] flag off the Zephyr one.

[josuah]

Here is a script to do everything on top of the appropriate LiteX and Zephyr forks: zephyr_on_litex_on_crosslink_nx_evn.txt

1. modify the hardware as described by LiteX:

   • Remove R18 and R19 and populate R15 and R17
   • Put FTDI UART on port B: FTProg or https://github.com/trabucayre/fixFT2232_ecp5evn

2. Run all script steps: sh zephyr_on_litex_on_crosslink_nx_evn.txt all

3. Connect to the LiteX shell

   litex_term /dev/ttyUSB1
   LiteX> boot 0x01000000
   uart$

[josuah]

All the submissions that are left are RFCs, the other ones were not essential. Nothing left here! The remaining [RFC]s can live on their own. Thank you for watching! :)