MIPS: add MT ASE support for micromips32

These instructions are descripted in MD00768.

MIPS® Architecture for Programmers
Volume IV-f: The MIPS® MT Module for
the microMIPS32™ Architecture

Document Number: MD00768
Revision 1.12
July 16, 2013

https://s3-eu-west-1.amazonaws.com/downloads-mips/documents/MD00768-1C-microMIPS32MT-AFP-01.12.pdf