8146629: Make phase->is_IterGVN() accessible from Node::Identity and Node::Value
Summary: Change arguments of Node::Identity() and Node::Value() from PhaseTransform* to PhaseGVN*.
Reviewed-by: kvn, roland

8001532: C2 node files refactoring
Summary: Split C2 node files into cast, convert, countbits, intrinsic, move, narrowptr and opaquenode classes
Reviewed-by: kvn, morris