[llvm] [AMDGPU][MC] Support src modifiers for v_mov_b32 and v_movrel* instructions (PR #76498)

[Matt Arsenault via llvm-commits]

arsenm wrote:

Do these actually work? I vaguely recall seeing a note in a manual that these were ignored. It's possible this changed in newer generations 

https://github.com/llvm/llvm-project/pull/76498