[llvm] AMDGPU: Try to constrain av registers to VGPR to enable ds_write2 formation (PR #156400)

[Stanislav Mekhanoshin via llvm-commits]

================
@@ -172,9 +172,10 @@ body:             |
 
     ; GCN-LABEL: name: no_merge_flat_load_dword_agpr_with_vgpr
----------------
rampitec wrote:

The name of the test 'no_merge_...' is now incorrect.

https://github.com/llvm/llvm-project/pull/156400