[ARM] Add support for MVFR2 which is new in ARMv8

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194416 91177308-0d34-0410-b5e6-96231b3b80d8
CalcSpillWeights: allow overidding the spill weight normalizing function

This will enable the PBQP register allocator to provide its own normalizing function.

No functionnal change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194417 91177308-0d34-0410-b5e6-96231b3b80d8