[X86] Simplify function isDataInvariant by using X86MnemonicTables

This is not a NFC change b/c we add more instructions like
IMUL16/32/64r, MOV16ao16 and MOV16rr_REV etc to the list.
But I think it's reasonable.

Reviewed By: Amir

Differential Revision: https://reviews.llvm.org/D122063