opcodes/loongarch: print unrecognized insn words with the .word directive

For better round-trip fidelity and readability in general.

gas/ChangeLog:

	* testsuite/gas/loongarch/uleb128.d: Update test case.
	* testsuite/gas/loongarch/raw-insn.d: New test.
	* testsuite/gas/loongarch/raw-insn.s: Likewise.

opcodes/ChangeLog:

	* loongarch-dis.c (disassemble_one): Print ".word" if !opc.

Signed-off-by: WANG Xuerui <git@xen0n.name>