[llvm] [AMDGPU] SIPeepholeSDWA: Handle V_CNDMASK_B32_e64 (PR #137930)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

lgtm except there are still tests using undef flags on operands which really have defs 

https://github.com/llvm/llvm-project/pull/137930