Beginning of expanding all current mips16 macro/pseudo instruction sequences.

This expansion will be moved to expandISelPseudos as soon as I can figure
out how to do that. There are other instructions which use this 
ExpandFEXT_T8I816_ins and as soon as I have finished expanding them all,
I will delete the macro asm string text so it has no way to be used
in the future.

llvm-svn: 175413