[mips][mt][2/7] Implement .module and .set directives for the MT ASE.

This patch implements the .module and .set directives for the MT ASE,
notably that .module sets the relevant flags in .MIPS.abiflags and .set
doesn't.

Reviewers: slthakur, atanasyan

Differential Revision: https://reviews.llvm.org/D35249

llvm-svn: 307716