[llvm] [X86][MC] Support encoding/decoding for PUSHP/POPP (PR #73092)

[Shengchen Kan via llvm-commits]

KanRobert wrote:

> Just curious, all combinations are from 0x50 to 0x5F, can we test them all, or it is really redundant?

The logic for 0x50~0x5F is about the format `AddRegFrm` and already tested with legacy PUSH/POP.  So I think it's redundant.

https://github.com/llvm/llvm-project/pull/73092