aarch64: Add DSB instruction Armv8.7-a variant

aarch64: Add DSB instruction Armv8.7-a variant

This patch adds new variant (nXS) of DSB memory barrier instruction
available in Armv8.7-a. New nXS variant has different encoding in
comparison with pre Armv8.7-a DSB memory barrier variant thus new
instruction and new operand was added.

DSB memory nXS barrier variant specifies the limitation on the barrier
operation. Allowed values are:

	DSB SYnXS|#28
	DSB ISHnXS|#24
	DSB NSHnXS|#20
	DSB OSHnXS|#16

Please note that till now,  for barriers, barrier operation was encoded in
4-bit unsigned immediate CRm field (in the range 0 to 15).
For DSB memory nXS barrier variant, barrier operation is a 5-bit unsigned
assembly instruction immediate, encoded in instruction in two bits CRm<3:2>:

		CRm<3:2>  #imm
		  00       16
		  01       20
		  10       24
		  11       28

This patch extends current AArch64 barrier instructions with above mapping.

Notable patch changes include:
+ New DSB memory barrier variant encoding for Armv8.7-a.
+ New operand BARRIER_DSB_NXS for above instruction in order to
distinguish between existing and new DSB instruction flavour.
+ New set of DSB nXS barrier options.
+ New instruction inserter and extractor map between instruction
immediate 5-bit value and 2-bit CRm field of the instruction itself (see
FLD_CRm_dsb_nxs).
+ Regeneration of aarch64-[asm|dis|opc]-2.c files.
+ Test cases to cover new instruction assembling and disassembling.

For more details regarding DSB memory barrier instruction and its
Armv8.7-a flavour please refer to Arm A64 Instruction set documentation
for Armv8-A architecture profile, see document pages 132-133 of [0].

	[0]: https://developer.arm.com/docs/ddi0596/i

gas/ChangeLog:

2020-10-23  Przemyslaw Wirkus  <przemyslaw.wirkus@arm.com>

	* NEWS: Docs update.
	* config/tc-aarch64.c (parse_operands): Add
	AARCH64_OPND_BARRIER_DSB_NXS handler.
	(md_begin): Add content of aarch64_barrier_dsb_nxs_options to
	aarch64_barrier_opt_hsh hash.
	* testsuite/gas/aarch64/system-4-invalid.d: New test.
	* testsuite/gas/aarch64/system-4-invalid.l: New test.
	* testsuite/gas/aarch64/system-4-invalid.s: New test.
	* testsuite/gas/aarch64/system-4.d: New test.
	* testsuite/gas/aarch64/system-4.s: New test.

include/ChangeLog:

2020-10-23  Przemyslaw Wirkus  <przemyslaw.wirkus@arm.com>

	* opcode/aarch64.h (enum aarch64_opnd): New operand
	AARCH64_OPND_BARRIER_DSB_NXS.
	(aarch64_barrier_dsb_nxs_options): Declare DSB nXS options.

opcodes/ChangeLog:

2020-10-23  Przemyslaw Wirkus  <przemyslaw.wirkus@arm.com>

	* aarch64-asm.c (aarch64_ins_barrier_dsb_nxs): New inserter.
	* aarch64-asm.h (AARCH64_DECL_OPD_INSERTER): New inserter
	ins_barrier_dsb_nx.
	* aarch64-dis.c (aarch64_ext_barrier_dsb_nxs): New extractor.
	* aarch64-dis.h (AARCH64_DECL_OPD_EXTRACTOR): New extractor
	ext_barrier_dsb_nx.
	* aarch64-opc.c (aarch64_print_operand): New options table
	aarch64_barrier_dsb_nxs_options.
	* aarch64-opc.h (enum aarch64_field_kind): New field name FLD_CRm_dsb_nxs.
	* aarch64-tbl.h (struct aarch64_opcode): Define DSB nXS barrier
	Armv8.7-a instruction.
	* aarch64-asm-2.c: Regenerated.
	* aarch64-dis-2.c: Regenerated.
	* aarch64-opc-2.c: Regenerated.