[llvm] [RISCV] Set AllocationPriority in line with LMUL (PR #131176)

[Pengcheng Wang via llvm-commits]

https://github.com/wangpc-pp commented:

Thanks for looking at this! I tried this before but I can't remember why I dropped it (maybe it was simply because setting `AllocationPriority` couldn't fix #113489).
I do see some improvements and regressions but I don't think they are significant, this PR locates in improving compile-time since it avoids the later eviction? @lukel97 Can you also evaluate the performance please?

https://github.com/llvm/llvm-project/pull/131176