[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