LoongArch: Add support for the ud macro instruction

LoongArch: Add support for the ud macro instruction

In the "ud ui5" macro, the value of ui5 must be in the range 0–31. It
expands to "amswap.w $rd, $r1, $rj", where ui5 specifies the register
number for $rd in the amswap.w instruction, and $rd == $rj.

The test case have been adjusted to no longer report errors for illegal
operands of the amswap.w instruction.

gas/

	* config/tc-loongarch.c (check_this_insn_before_appending): No
	  longer check amswap.w.
	* testsuite/gas/loongarch/illegal-operand.l: Update.
	* testsuite/gas/loongarch/illegal-operand.s: Update.
	* testsuite/gas/loongarch/macro_ud.d: New test.
	* testsuite/gas/loongarch/macro_ud.s: New test.

include/

	* opcode/loongarch.h: Add new macro for amswap.w.

opcodes/

	* loongarch-opc.c: Add macro for ud.