[MIPS GlobalISel] Regbanks for G_SELECT. Select i64, f32 and f64 select
Select gprb or fprb when def/use register operand of G_SELECT is
used/defined by either:
copy to/from physical register or
instruction with only one mapping available for that use/def operand.
Integer s64 select is handled with narrowScalar when mapping is applied,
produced artifacts are combined away. Manually set gprb to all register
operands of instructions created during narrowScalar.
For selection of floating point s32 or s64 select it is enough to set
fprb of appropriate size and selectImpl will do the rest.
Differential Revision: https://reviews.llvm.org/D64350