build(deps): bump litex/deps/litex_boards from 929e55d to efc15a9

Bumps [litex/deps/litex_boards](https://github.com/litex-hub/litex-boards) from `929e55d` to `efc15a9`.
- [Commits](litex-hub/litex-boards@929e55d...efc15a9)

---
updated-dependencies:
- dependency-name: litex/deps/litex_boards
  dependency-type: direct:production
...

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