Support displaced stepping in aarch64-linux

Support displaced stepping in aarch64-linux

This patch is to support displaced stepping in aarch64-linux.  A
visitor is implemented for displaced stepping, and used to record
information to fixup pc after displaced stepping if needed.  Some
emit_* functions are converted to macros, and moved to
arch/aarch64-insn.{c,h} so that they can be shared.

gdb:

2015-10-12  Yao Qi  <yao.qi@linaro.org>

	* aarch64-linux-tdep.c: Include arch-utils.h.
	(aarch64_linux_init_abi): Call set_gdbarch_max_insn_length,
	set_gdbarch_displaced_step_copy_insn,
	set_gdbarch_displaced_step_fixup,
	set_gdbarch_displaced_step_free_closure,
	set_gdbarch_displaced_step_location,
	and set_gdbarch_displaced_step_hw_singlestep.
	* aarch64-tdep.c (struct displaced_step_closure): New.
	(struct aarch64_displaced_step_data): New.
	(aarch64_displaced_step_b): New function.
	(aarch64_displaced_step_b_cond): Likewise.
	(aarch64_register): Likewise.
	(aarch64_displaced_step_cb): Likewise.
	(aarch64_displaced_step_tb): Likewise.
	(aarch64_displaced_step_adr): Likewise.
	(aarch64_displaced_step_ldr_literal): Likewise.
	(aarch64_displaced_step_others): Likewise.
	(aarch64_displaced_step_copy_insn): Likewise.
	(aarch64_displaced_step_fixup): Likewise.
	(aarch64_displaced_step_hw_singlestep): Likewise.
	* aarch64-tdep.h (DISPLACED_MODIFIED_INSNS): New macro.
	(aarch64_displaced_step_copy_insn): Declare.
	(aarch64_displaced_step_fixup): Declare.
	(aarch64_displaced_step_hw_singlestep): Declare.
	* arch/aarch64-insn.c (emit_insn): Moved from
	gdbserver/linux-aarch64-low.c.
	(emit_load_store): Likewise.
	* arch/aarch64-insn.h (enum aarch64_opcodes): Moved from
	gdbserver/linux-aarch64-low.c.
	(struct aarch64_register): Likewise.
	(struct aarch64_memory_operand): Likewise.
	(ENCODE): Likewise.
	(can_encode_int32): New macro.
	(emit_b, emit_bcond, emit_cb, emit_ldr, emit_ldrsw): Likewise.
	(emit_tb, emit_nop): Likewise.
	(emit_insn): Declare.
	(emit_load_store): Declare.

gdb/gdbserver:

2015-10-12  Yao Qi  <yao.qi@linaro.org>

	* linux-aarch64-low.c (enum aarch64_opcodes): Move to
	arch/aarch64-insn.h.
	(struct aarch64_memory_operand): Likewise.
	(ENCODE): Likewise.
	(emit_insn): Move to arch/aarch64-insn.c.
	(emit_b, emit_bcond, emit_cb, emit_tb): Remove.
	(emit_load_store): Move to arch/aarch64-insn.c.
	(emit_ldr, emit_ldrb, emit_ldrsw, emit_nop): Remove.
	(can_encode_int32): Remove.