This patch adds a predicate to existing mips32 and mips64 so that those

instruction encodings can be excluded during mips16 processing.

This revision fixes the issue raised by Jim Grosbach.

bool hasStandardEncoding() const { return !inMips16Mode(); }

When micromips is added it will be

bool StandardEncoding() const { return !inMips16Mode()&&  !inMicroMipsMode(); }

No additional testing is needed other than to assure that there is no regression
from this patch.

Patch by Reed Kotler.

llvm-svn: 157234