These are identical but use microMIPS instructions instead of MIPS instructions.
Also, flatten the 'let AdditionalPredicates = [InMicroMips]' by using the
ISA_MICROMIPS adjective. Add tests for constant materialization.
Reviewers: atanasyan, abeserminji, smaksimovic
Differential Revision: https://reviews.llvm.org/D48275
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@335185 91177308-0d34-0410-b5e6-96231b3b80d8