[AArch64, 1/6] Enable ARMv8.5-A in gcc

This patch is part of a series that enables ARMv8.5-A in GCC and
adds Branch Target Identification Mechanism.

*** gcc/ChangeLog ***

2018-01-09  Sudakshina Das  <sudi.das@arm.com>

	* config/aarch64/aarch64-arches.def: Define AARCH64_ARCH for
	ARMv8.5-A.
	* gcc/config/aarch64/aarch64.h (AARCH64_FL_V8_5): New.
	(AARCH64_FL_FOR_ARCH8_5, AARCH64_ISA_V8_5): New.
	* gcc/doc/invoke.texi: Document ARMv8.5-A.

From-SVN: r267765