[GlobalISel][X86] Support G_STORE/G_LOAD operation

Summary:
1. Support pointer type as function argumnet and return value
2. G_STORE/G_LOAD - set legal action for i8/i16/i32/i64/f32/f64/vec128
3. RegisterBank - support typeless operations like G_STORE/G_LOAD, for scalar use GPR bank.
4. Support instruction selection for G_LOAD/G_STORE

Reviewers: zvi, rovka, ab, qcolombet

Reviewed By: rovka

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

Differential Revision: https://reviews.llvm.org/D30973

llvm-svn: 298609