[mips] Add '-mvirt', '-mno-virt', '-mginv', '-mno-ginv' options

'-mvirt'/'-mno-virt' enables/disables Virtualization ASE.
'-mginv'/'-mno-ginv' enables/disables GINV (Global Invalidate) ASE.

Differential revision: https://reviews.llvm.org/D48982

llvm-svn: 336798