[AArch64] Add ARMv8.2 instruction alias REV64.

[AArch64] Add ARMv8.2 instruction alias REV64.

This patch adds the alias REV64 <Rd>, <Rs> as an alias for REV <Rd>,
<Rs>. However, REV is still the preferred form for the instruction.

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

	* gas/aarch64/alias-2.d: Add tests for REV.
	* gas/aarch64/alias-2.s: Likewise.

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

	* aarch64-asm-2.c: Regenerate.
	* aarch64-dis-2.c: Regenerate.
	* aarch64-opc-2.c: Regenerate.
	* aarch64-tbl.h (aarchr64_opcode_table): Update "rev", add
	"rev64".