Add lattice_certus_nx_versa - #757

Thanks @gatecat! Since you LiteDRAM support is merged, do you also want to merge this one? This seems perfectly good enough as a first PR for to support this board and we could enhance later with more specific PR. Happy to do the cosmetic changes (if required) and ensuring it passes CI if OK for you.

Added follow-up commit be7528e:

• aligned the platform/target structure, imports, comments, and argument formatting with current LiteX-Boards conventions;
• removed copied programmer options that advertised unsupported Radiant/OpenOCD programming, and exposed the standard ecpprog --load/--flash flow;
• declared the power-on-reset clock domain as resetless;
• named the active-low buttons/LEDs accordingly and corrected the LED chaser polarity;
• regenerated the README board list and board inventory required by CI.

Validation:

• all board consistency, parser, README, and inventory checks pass;
• the 14 focused CI guardrail tests pass;
• --build --no-compile passes with Radiant for the base, DDR3, SPI flash, and combined DDR3 + SPI flash configurations;
• the base configuration also passes with Oxide;
• the PR merges cleanly with current master, with the checks and combined configuration revalidated on the merged tree.

No full bitstream compilation was needed for this review.

Thanks, this all seems reasonable to me! I will probably submit follow-ups at some point with an x4 CRG (when I get that to work) and also the RGMII/SGMII pins.

@gatecat: Good, let's merge then, thanks!