[mips][msa] Fix infinite loop for mips.nori.b intrinsic

When value of immediate in `mips.nori.b` is 255 (which has all ones in
binary form as 8bit integer) DAGCombiner and Legalizer would fall in an
infinite loop. DAGCombiner would try to simplify `or %value, -1` by
turning `%value` into UNDEF. Legalizer will turn it back into `Constant<0>`
which would then be again turned into UNDEF by DAGCombiner. To avoid this
loop we make UNDEF legal for MSA int types on Mips.

Patch by Mirko Brkusanin.

Differential Revision: https://reviews.llvm.org/D67280

llvm-svn: 371607