[ARM] Add ARMv8.2 architecture feature and command line option.

[ARM] Add ARMv8.2 architecture feature and command line option.

ARMv8.2 is an architectural extension of ARMv8. This patch adds an
architecture feature macro for ARMv8.2 to the binutils ARM target
with GAS command line option -march=armv8.2-a.

gas/
2015-11-19  Matthew Wahab  <matthew.wahab@arm.com>

	* config/tc-arm.c (arm_archs): Add "armv8.2-a".
	* doc/c-arm.texi (-march): Add "armv8.2-a".

include/opcode/
2015-11-19  Matthew Wahab  <matthew.wahab@arm.com>

	* arm.h (ARM_EXT2_V8_2A): New.
	(ARM_ARCH_V8_2A): New.

Change-Id: I9e0f50e3c6cea24e6b87b8b862fd4e1cdcc1052e