The `MipsAsmParser::loadImmediate` can load immediates of various sizes
into a register. Idea of this change is to use `loadImmediate` in the
`MipsAsmParser::expandMemInst` method to load offset into a register and
then call required load/store instruction.
The patch removes separate `expandLoadInst` and `expandStoreInst`
methods and does everything in the `expandMemInst` method to escape code
duplication.
Differential Revision: https://reviews.llvm.org/D47316
llvm-svn: 333774
e80c3ce9cc