[MIPS GlobalISel] Lower pointer arguments

Add support for lowering pointer arguments.
Changing type from pointer to integer is already done in
MipsTargetLowering::getRegisterTypeForCallingConv.

Patch by Petar Avramovic.

Differential Revision: https://reviews.llvm.org/D49419


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337912 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed