[llvm] [RISCV][RegAlloc] Add getCSRFirstUseCost for RISC-V (PR #131349)

[Luke Lau via llvm-commits]

lukel97 wrote:

> It all makes sense to me, I just wonder if the value 64 is too high since the value on AArch64 is 5. I don't see any big arch difference between RISC-V and AArch64 since they are both arch for RISC CPUs.
> 
> Maybe @lukel97 you can issue another several runs with different costs?

Oh I see what you mean, I'll kick off a run with 5 and see how that compares

https://github.com/llvm/llvm-project/pull/131349