[mips] Add madd4 subtarget feature

Addition of a feature and a predicate used to control generation of madd.fmt
and similar instructions.

Patch by Stefan Maksimovic.

Differential Revision: https://reviews.llvm.org/D33400


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304801 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed