[llvm] [AMDGPU] Change the immediate operand of s_waitcnt_depctr / s_wait_alu (PR #169378)

[Jay Foad via llvm-commits]

jayfoad wrote:

> However, I wonder if we couldn't just create a representation of the unused bits that work the same as real counters, e.g. depctr_unused. Then they would default to 1 (for GFX10.3 onward)? But maybe I misunderstood the `DepCtrInfo` table code.

We could but that would break SP3 compatibility in the sense that e.g. `s_waitcnt_depctr depctr_va_vdst(0)` would start assembling to BFA30FFF instead of BFA30F9F.

https://github.com/llvm/llvm-project/pull/169378