[AArch64] Fix missing architecture checks for ARMv8.2 system registers.

[AArch64] Fix missing architecture checks for ARMv8.2 system registers.

Some of the RAS system registers added to binutils as part of the ARMv8.2
support are missing the feature checks to warn when they aren't
supported by the target.

This patch adds the missing feature checks with a test to check that
the correct warnings are given for all the ARMv8.2 system registers.

gas/
2016-01-14  Matthew Wahab  <matthew.wahab@arm.com>

	* testsuite/gas/aarch64/illegal-sysreg-2.l: New.
	* testsuite/gas/aarch64/illegal-sysreg-2.d: New.

opcodes/
2016-01-14  Matthew Wahab  <matthew.wahab@arm.com>

	* aarch64-opc.c (aarch64_sys_reg_supported_p): Merge conditionals
	testing for RAS support.  Add checks for erxfr_el1, erxctlr_el1,
	erxtatus_el1 and erxaddr_el1.

Change-Id: I66b590ea49c1eb6b0e5c93e0dc2bc9c4e79a52fe