Improve gas error messages for invalid instructions.

Improve gas error messages for invalid instructions.
	* cpu-ia64-opc.c (elf64_ia64_operands}: Fix typo: error string for
	C8 said "1" instead of "8".  Clarify error string for IMM22:
	"signed integer" instead of just "integer".
	* config/tc-ia64.c (enum operand_match_result): New type.
	(operand_match): Change return type to operand_match_result.
	Fix all returns appropriately, adding support for returning the
	out-of-range result.
	(parse_operands): New locals result, error_pos, out_of_range_pos,
	curr_out_of_range_pos.  Rewrite operand matching loop to give better
	error messages.
	* ia64-opc-d.c (ia64_opcodes_d): Break the "add" pattern into two
	separate variants: one for IMM22 and the other for IMM14.
	* ia64-asmtab.c: Regenerate.