[llvm] AMDGPU: Start fixing inconsistencies in usage of SubtargetPredicate (PR #96337)

[Matt Arsenault via llvm-commits]

================
@@ -1227,12 +1227,12 @@ defm BUFFER_ATOMIC_PK_ADD_F16 : MUBUF_Pseudo_Atomics_NO_RTN <
   "buffer_atomic_pk_add_f16", VGPR_32, v2f16
 >;
 
-let OtherPredicates = [HasAtomicFaddRtnInsts] in
+let SubtargetPredicate = HasAtomicFaddRtnInsts in
----------------
arsenm wrote:

I think SubtargetPredicate should be the "primary" predicate attached to some subtarget feature, for whether the instruction exists at all. The OtherPredicates are for misc. other things, like xnack is enabled (or in the buffer cases, the gfx12 vbuffer encoding). 

https://github.com/llvm/llvm-project/pull/96337