[llvm] [AMDGPU] Fix op_sel settings for v_cvt_scale32_* and v_cvt_sr_* (PR #151286)

[Stanislav Mekhanoshin via llvm-commits]

rampitec wrote:

Ideally it should backport byte_sel modifier from gfx1250 and deal with encoding peculiarities at the MC layer.

https://github.com/llvm/llvm-project/pull/151286