[llvm] [RISCV] Add more files to .github/CODEOWNERS (PR #65234)

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

Or perhaps we should follow the suggestion in https://discourse.llvm.org/t/input-needed-teams-for-pull-request-subscriptions/73116/79? That's effectively what my Herald rule did (though case-insensitive).

https://github.com/llvm/llvm-project/pull/65234