Tidy ppc476 opcodes

Tidy ppc476 opcodes

PPC_OPCODE_440 being set for ppc476 meant that many opcodes needed to
be deprecated for ppc476.  There are far fewer to add specially for
ppc476 if PPC_OPCODE_440 is not set for ppc476.

	* ppc-dis.c (ppc_opts <476>): Remove PPC_OPCODE_440.
	* ppc-opc.c (MULHW): Add PPC_OPCODE_476.
	(powerpc_opcodes): Adjust PPC440, PPC464 and PPC476 insns to suit
	removal of PPC_OPCODE_440 from ppc476 cpu selection bits.