[AArch64][PATCH 1/2] Add support for RAS instruction ESB.

[AArch64][PATCH 1/2] Add support for RAS instruction ESB.

The ARMv8.2 RAS extension adds a new barrier instruction ESB as an alias
and the preferred form of HINT 16.

This patch adds an architectural feature flag for the RAS extension and
includes it in the features selected enabled by -march=armv8.2-a. It
also adds the ESB instruction, making it available whenever the RAS
feature is enabled.

Because ESB is the preferred form and because the target architecture
isn't available to the disassembler, HINT 16 will be disassembled as ESB
even when the target has no support for the RAS extension.

gas/testsuite/
2015-12-10  Matthew Wahab  <matthew.wahab@arm.com>

	* gas/aarch64/system-2.d: New.
	* gas/aarch64/system-2.s: New.
	* gas/aarch64/system.d: Adjust expected output for HINT 16.

include/opcode/
2015-12-10  Matthew Wahab  <matthew.wahab@arm.com>

	* aarch64.h (AARCH64_FEATURE_RAS): New.
	(AARCH64_ARCH_V8_2): Add AARCH64_FEATURE_RAS.

opcodes/
2015-12-10  Matthew Wahab  <matthew.wahab@arm.com>

	* aarch64-asm-2.c: Regenerate.
	* aarch64-dis-2.c: Regenerate.
	* aarch64-tbl.h (aarch64_feature_ras): New.
	(RAS): New.
	(aarch64_opcode_table): Add "esb".

Change-Id: Id4713917da15cca3b977284f43febd1c9b3d9faf