[llvm] AMDGPU/GlobalISel: Implement RegBankLegalizeRules for amdgcn_log, amdgcn_rcp, and amdgcn_sqrt (PR #195099)

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anjenner wrote:

64-bit log doesn't seem to exist - I've removed that from RegBankLegalizeRules. The others I have added tests for and verified that the results look sensible. I'll add 64-bit and divergent tests for exp, rsq and sqrt in a separate PR.

https://github.com/llvm/llvm-project/pull/195099