PowerPC register expression checks

This stops powerpc gas blithely accepting such nonsense as
"addi %f4,%cr3,%r31".

	PR 21118
gas/
	* NEWS: Mention powerpc register checks.
	* config/tc-ppc.c (struct pd_reg): Make value a short.  Add flags.
	(pre_defined_registers): Delete fpscr and pmr entries.  Set
	register type in flags.
	(cr_names): Set type in flags.
	(reg_name_search): Return pointer to struct pd_reg rather than value.
	(register_name): Adjust to suit.  Set X_md from flags.
	(ppc_parse_name): Likewise.
	(ppc_optimize_expr): New function.
	(md_assemble): Verify expresion reg flags match operand.
	* config/tc-ppc.h (md_optimize_expr): Define.
	(ppc_optimize_expr): Declare.
include/
	* opcode/ppc.h (PPC_OPERAND_*): Reassign values, regs first.
	(PPC_OPERAND_SPR, PPC_OPERAND_GQR): Define.
opcodes/
	* ppc-opc.c (powerpc_operands): Flag SPR, SPRG and TBR entries
	with PPC_OPERAND_SPR.  Flag PSQ and PSQM with PPC_OPERAND_GQR.