[AArch64] Split zero cycle feature more granularly

[AArch64] Split zero cycle feature more granularly

Split the `zcz` feature into specific ones got GP and FP registers, `zcz-gp`
and `zcz-fp`, respectively, while retaining the original feature option to
mean both.

Differential revision: https://reviews.llvm.org/D52621

llvm-svn: 343354