[llvm] [AMDGPU] Update VOP instructions for GFX12 (PR #74853)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Just to give some background to Mirko's questions:
> 
> * In GFX11 the 64-bit shifts V_ASHRREV_I64, V_LSHLREV_B64 and V_LSHRREV_B64 are all VOP3 only.
> * In GFX12 V_LSHLREV_B64 moved to VOP2 but V_ASHRREV_I64 and V_LSHRREV_B64 are still VOP3 only.

This is confusing, maybe deserves a comment 

https://github.com/llvm/llvm-project/pull/74853