[X86] Improve selection of the mov instruction in FrameLowering

MOV64ri results in a significantly longer encoding, and use of this
operator is fairly avoidable as we can always check the size of the
immediate we're using.

This is an updated version of D99045.

Co-authored-by: Simonas Kazlauskas <git@kazlauskas.me>

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D116458