Add support for the Fomu board

[mithro]

It would be awesome if the SaxonSoC supported the Tomu FPGA (Fomu). This would be an awesome introduction into to pure SpinalHDL design.

Happy to send people boards.

[lawrie]

Fomu has been supported for some time - see https://github.com/SpinalHDL/SaxonSoc/blob/dev/hardware/scala/saxon/board/fomu/FomuMinimal.scala

I was planning to add support for Xip on the board as well and asked Sean Cross a question about how to get the Risc-V program into flash memory, but then I got my Ulx3s boards and have been mainly working on Linux on those.

Other operating systems such as Zephyr of FreeRTOS might run using SaxonSoc on the board.

[Dolu1990]

Would probably need to update it. @lawrie Is the ram inferred using the big 32 KB blocks ?

[roman3017]

It seems Fomu is using BmbOnChipRamGenerator instead of BmbIce40SpramGenerator. The later is being used only by Ice40up5kbevn.