[mips] Continue splitting Instruction.Predicates into smaller lists and re-join them with !listconcat

Summary:
Move IsGP64bit into GPRPredicates, and IsFP64bit/NotFP64bit into FGRPredicates

No functional change (confirmed by diffing tablegen-erated files).

Depends on D3639

Reviewers: vmedic

Reviewed By: vmedic

Differential Revision: http://reviews.llvm.org/D3640

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208201 91177308-0d34-0410-b5e6-96231b3b80d8