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

[Evgenii Kudriashov via llvm-commits]

e-kud wrote:

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

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