[AArch64][libopcode] Add support for PAN architecture extension

[AArch64][libopcode] Add support for PAN architecture extension

The ARMv8.1 architecture introduced the Privileged Access Never extension. This
adds a processor state field PSTATE.PAN which can be accessed using the MRS/MSR
instructions.

This patch adds support for the PAN architecture feature and processor state
field to libopcode.

include/opcode
2015-06-01  Matthew Wahab  <matthew.wahab@arm.com>

	* aarch64.h (AARCH64_FEATURE_PAN): New.
	(aarch64_sys_reg_supported_p): Declare.
	(aarch64_pstatefield_supported_p): Declare.

opcodes/
2015-06-01  Matthew Wahab  <matthew.wahab@arm.com>
	* aarch64-opc.c (F_ARCHEXT): New.
	(aarch64_sys_regs): Add "pan".
	(aarch64_sys_reg_supported_p): New.
	(aarch64_pstatefields): Add "pan".
	(aarch64_pstatefield_supported_p): New.