[mips] Correct the definitions of some control instructions

Correct the definitions of ei, di, eret, deret, wait, syscall and break.
Also provide microMIPS specific aliases to match the MIPS aliases.

Additionally correct the definition of the wait instruction so that
it is present in the instruction mapping tables.

Reviewers: smaksimovic, abeserminji, atanasyan

Differential Revision: https://reviews.llvm.org/D45939

llvm-svn: 330952