[X86] Remove patterns for ADD/AND/OR/SUB/XOR/CMP with immediate 8 and optimize...

[X86] Remove patterns for ADD/AND/OR/SUB/XOR/CMP with immediate 8 and optimize during MC lowering, NFCI

This is follow-up of D150107.

In addition, the function `X86::optimizeToFixedRegisterOrShortImmediateForm` can be
shared with project bolt and eliminates the code in X86InstrRelaxTables.cpp.

Differential Revision: https://reviews.llvm.org/D150949