[llvm] [AMDGPU][CodeGen] Don't always create `S_SET_VGPR_MSB` after `S_SETREG_B32` (PR #210042)

[Jay Foad via llvm-commits]

jayfoad wrote:

> On encountering a `S_SETREG_IMM32_B32(MODE)` with size>12, offset==0,

Jus curious: how often do we encounter this case in real world code?

https://github.com/llvm/llvm-project/pull/210042