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

[Jay Foad via llvm-commits]

jayfoad wrote:

> Is there any way you can keep the undefined/reserved bits in the mask as 1?

Yes, I could abandon this patch or break compatibility with SP3. But the whole point of this patch is that I thought on the whole it was better to change the bits to 0 and keep compatibility with SP3.

> While it's probably fine if they are 0 they have always been set, so we need to double check there aren't any unintended consequences of not setting them.

I can run some testing on real hardware to smoke out any unintended consequences.

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