[GlobalISel][X86] support G_FRAME_INDEX instruction selection.

    Summary:
    G_LOAD/G_STORE, add alternative RegisterBank mapping.
    For G_LOAD, Fast and Greedy mode choose the same RegisterBank mapping (GprRegBank ) for the G_GLOAD + G_FADD , can't get rid of cross register bank copy GprRegBank->VecRegBank.

    Reviewers: zvi, rovka, qcolombet, ab

    Reviewed By: zvi

    Subscribers: llvm-commits, dberris, kristof.beyls, eladcohen, guyblank

    Differential Revision: https://reviews.llvm.org/D30979

llvm-svn: 298907