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

[Janek van Oirschot via llvm-commits]

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@@ -238,18 +242,40 @@ enum : int32_t {
 
 // Kernel descriptor. Must be kept backwards compatible.
 struct kernel_descriptor_t {
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JanekvO wrote:

As far as I can tell, the code I changed in this patch are the only users of this struct but I can do whatever's preferred: a MCExpr-ified copy to exist in the AMDGPU directory or modify this struct to only contain the necessities.

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