[llvm] [AMDGPU][MC] Check availability of certain registers (PR #214973)

[Shilei Tian via llvm-commits]

shiltian wrote:

* #214973 👈
* `main`

<h2></h2>

This stack of pull requests is managed by <a href="https://github.com/shiltian/sgh"><b>sgh</b></a>.
<!-- SGH-MANAGED-COMMENT: DO NOT EDIT OR DELETE THIS COMMENT -->

https://github.com/llvm/llvm-project/pull/214973