AArch64: Refactor verifiers to make more general.

AArch64: Refactor verifiers to make more general.

The current verifiers only take an instruction description and encoded value as
arguments.  This was enough when the verifiers only needed to do simple checking
but it's insufficient for the purposes of validating instruction sequences.

This patch adds the required arguments and also a flag to allow a verifier to
distinguish between whether it's being run during encoding or decoding.  It also
allows for errors and warnings to be returned by a verifier instead of a simple
pass/fail.

include/

	* opcode/aarch64.h (struct aarch64_opcode): Expand verifiers to take
	more arguments.

opcodes/

	* aarch64-dis.c (aarch64_opcode_decode): Update verifier call.
	* aarch64-opc.c (verify_ldpsw): Update arguments.