[AArch64] Let aliased instructions be their preferred form.

Although the AArch64 backend supports aliased instructions, the aliasing
forms are always preferred over the real instruction. This makes it
awkward to handle instructions which have aliases but which are their
own preferred form.

This patch includes the instruction being aliased in the list of
alternatives which is searched when considering which form to use.

opcodes/
2015-11-27  Matthew Wahab  <matthew.wahab@arm.com>

	* aarch64-asm-2.c: Regenerate.
	* aarch64-dis-2.c: Regenerate.
	* aarch64-dis.c: Weaken assert.
	* aarch64-gen.c: Include the instruction in the list of its
	possible aliases.

Change-Id: I1f23eb25fccef76a64d3d732d58761bd25fad94e