[x86] improve CMOV codegen by pushing add into operands, part 2

This is a minimum extension of D106607 to allow folding for
2 non-zero constantsi that can be materialized as immediates..

In the reduced test examples, we save 1 instruction by rolling
the constants into LEA/ADD. In the motivating test from the bullet
benchmark, we absorb both of the constant moves into add ops via
LEA magic, so we reduce by 2 instructions.

Differential Revision: https://reviews.llvm.org/D106684