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

[Philip Reames via llvm-commits]

preames wrote:

> Results on rva22u64_v -O3 -flto: https://lnt.lukelau.me/db_default/v4/nts/311

Looks like we saw a small improvement in x264 and not much else.  That's actually a bit better than I'd expected; definitely nothing problematic at least.

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