[mips] Eliminate the usage of hasStdEnc in MipsPat.

Instead, the pattern is tagged with the correct predicate when
it is declared. Some patterns have been duplicated as necessary.

Patch by Simon Dardis.

Differential revision: https://reviews.llvm.org/D48365

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337171 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed