[AArch64] Reject invalid immediate operands to MSR PAN

[AArch64] Reject invalid immediate operands to MSR PAN

The support for accessing the ARMv8.1 PSTATE field PAN allows
instructions of the form MSR PAN, #<imm> with <imm> any unsigned 4-bit
integer. However, the architecture specification requires that the
immediate is either 0 or 1.

This patch implements the constraint on the immediate, generating an
error if the immediate operand is invalid, and adds tests for the
illegal forms.

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

	* aarch64-opc.c (operand_general_constraint_met_p): Check validity
	of MSR PAN immediate operand.

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

	* gas/aarch64/pan-illegal.d: New.
	* gas/aarch64/pan-illegal.l: New.
	* gas/aarch64/pan.s: Add tests for invalid immediates.

Change-Id: Ibb3056c975eb792104da138d94594224f56a993e