* gas/config/tc-arm.c (asm_barrier_opt): Add arch field.

	* gas/config/tc-arm.c (asm_barrier_opt): Add arch field.
	(mark_feature_used): New function.
	(parse_barrier): Check specified option is valid for the
	specified architecture.
	(UL_BARRIER): New macro.
	(barrier_opt_names): Update for new barrier options.
	* gas/testsuite/gas/arm/armv8-a-barrier.s: New testcase.
	* gas/testsuite/gas/arm/armv8-a-barrier-arm.d: Likewise.
	* gas/testsuite/gas/arm/armv8-a-barrier-thumb.d: Likewise.
	* opcodes/arm-dis.c (data_barrier_option): New function.
	(print_insn_arm): Use data_barrier_option.
	(print_insn_thumb32): Use data_barrier_option.