include/opcode/

include/opcode/
	* mips.h (OP_OPTIONAL_REG): New mips_operand_type.
	(mips_optional_operand_p): New function.

opcodes/
	* mips-formats.h (OPTIONAL_REG, OPTIONAL_MAPPED_REG): New macros.
	* micromips-opc.c (decode_micromips_operand): Use OPTIONAL_REG
	and OPTIONAL_MAPPED_REG.
	* mips-opc.c (decode_mips_operand): Likewise.
	* mips16-opc.c (decode_mips16_operand): Likewise.
	* mips-dis.c (print_insn_arg): Handle OP_OPTIONAL_REG.

gas/
	* config/tc-mips.c (operand_reg_mask, match_operand): Handle
	OP_OPTIONAL_REG.
	(mips_ip, mips16_ip): Use mips_optional_operand_p to check
	for optional operands.