[AArch64] Add ARMv8.2 instructions BFC and REV64.

[AArch64] Add ARMv8.2 instructions BFC and REV64.

ARMv8.2 adds two new instructions: BFC as an alias for BFM and REV64 as
an alias for REV. This patch set adds support for these to binutils,
enabled when the -march=armv8.2-a is given. It depends on the support
for an instruction being its preferred form which was added in an
earlier patch.

This patch adds the alias BFC <Rd>, #<imm>, #<width> as the preferred
form for BFM when the source is a zero register and the conditions for
using the BFI form are met (in other words, BFC is the preferred form
for BFI <Rd>, <Rs>, #<imm>, #<width> when the <Rs> is a zero register).

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

	* gas/aarch64/alias-2.d: New.
	* gas/aarch64/alias-2.s: New.

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

	* aarch64.h (aarch64_op): Add OP_BFC.

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

	* aarch64-asm-2.c: Regenerate.
	* aarch64-asm.c (convert_bfc_to_bfm): New.
	(convert_to_real): Add case for OP_BFC.
	* aarch64-dis-2.c: Regenerate.
	* aarch64-dis.c: (convert_bfm_to_bfc): New.
	(convert_to_alias): Add case for OP_BFC.
	* aarch64-opc-2.c: Regenerate.
	* aarch64-opc.c (operand_general_constraint_met_p): Weaken assert
	to allow width operand in three-operand instructions.
	* aarch64-tbl.h (QL_BF1): New.
	(aarch64_feature_v8_2): New.
	(ARMV8_2): New.
	(aarch64_opcode_table): Add "bfc".