[llvm] [AMDGPU] MCExpr-ify MC layer kernel descriptor (PR #80855)

[Janek van Oirschot via llvm-commits]

JanekvO wrote:

Would like to add a test that demonstrates the propagation to kernel descriptor expressions but will mean this depends on #82022.

> This would solve the issue of the day, but doesn't solve the general external object linking case. We need some way to refer to a specific external symbol's resource uses for that

What I've got so far mimics the behaviour of AMDGPUResourceUsageInfo which take the module scope maximums in case of external calls. Can't say I've looked into the scenario of linking, I wonder how nicely the required MCExpr operations such as the ones introduced in #82022 will play with relocations (if at all).

https://github.com/llvm/llvm-project/pull/80855