[AArch64][binutils] Add support for ARMv8.2 PSTATE.UAO.

[AArch64][binutils] Add support for ARMv8.2 PSTATE.UAO.

ARMv8.2 adds a new control bit PSTATE.UAO. This patch adds support for
this bit to binutils, following the same basic pattern as for
PSTATE.PAN. The new control bit is only available when -march=armv8.2-a
is specified.

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

	* gas/aarch64/uao-directive.d: New.
	* gas/aarch64/uao.d: New.
	* gas/aarch64/uao.s: New.

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

	* aarch64-opc.c (aarch64_sys_regs): Add "uao".
	(aarch64_sys_reg_supported_p): Add comment.  Add checks for "uao".
	(aarch64_pstatefields): Add "uao".
	(aarch64_pstatefield_supported_p): Add checks for "uao".

Change-Id: Id571628ac5227b78aaf1876e85d15d7b6c0a2896