[MIPS GlobalISel] Lower i8 and i16 arguments

Lower integer arguments smaller than i32.
Support both register and stack arguments.
Define setLocInfo function for setting LocInfo field in ArgLocs vector.

Patch by Petar Avramovic.

Differential Revision: https://reviews.llvm.org/D51031


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340572 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed