[AArch64] Implement workaround for ARM Cortex-A53 erratum 835769

[AArch64] Implement workaround for ARM Cortex-A53 erratum 835769

	* config/aarch64/aarch64.h (FINAL_PRESCAN_INSN): Define.
	(ADJUST_INSN_LENGTH): Define.
	* config/aarch64/aarch64.opt (mfix-cortex-a53-835769): New option.
	* config/aarch64/aarch64.c (is_mem_p): New function.
	(is_memory_op): Likewise.
	(aarch64_prev_real_insn): Likewise.
	(is_madd_op): Likewise.
	(dep_between_memop_and_curr): Likewise.
	(aarch64_madd_needs_nop): Likewise.
	(aarch64_final_prescan_insn): Likewise.
	* doc/invoke.texi (AArch64 Options): Document -mfix-cortex-a53-835769
	and -mno-fix-cortex-a53-835769 options.

From-SVN: r216075