[Mips][msa] Value types for MSA support.

Added v8f16 to ValueTypes.h, ValueTypes.cpp, ValueTypes.td, 
and CodeGenTarget.cpp

Patch by Daniel Sanders


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188326 91177308-0d34-0410-b5e6-96231b3b80d8