The patch adds CodeGen support for microMIPS32r6 SEL.*, SELEQZ, SELNEZ, SELEQZ.* and SELNEZ.* instructions:
- added DAG pattern definitions for proper selection of instructions
- separated microMIPS32r6 instructions from equivalent MIPS32r6 instructions using NotInMicroMips predicate
- added relation between microMIPS32r6 and equivalent MIPS32r6 instructions
- fixed wrong instruction names
- updated .ll files with tests for microMIPS32r6 select instructions