[RISCV] Add MC support of RISCV zcmp Extension

This patch add the instructions of zcmp extension.

Instructions in zcmp extension try to optimise `mv` inst and the prologue & epilogue in functions

co-author: @Scott Egerton, @ZirconLiu, @Lukacma, @Heda Chen, @luxufan, @heyiliang, @liaochunyu

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D132819