[clang] [llvm] [RISCV][P-ext] Add packed multiply high parts accumulate intrinsics (PR #224261)

[via llvm-commits]

StarryCSF wrote:

Friendly ping  @topperc  @sihuan  
This PR has been open for some time and has not been further reviewed yet. I have merged the latest main into this branch and resolved the conflict with pmulh/mulh work (no functional changes; all tests passed locally), so it should be combinable
Now, can you take another look if there's a chance? Thank you

https://github.com/llvm/llvm-project/pull/224261