[AArch64] Cleanup logic around aarch64_final_prescan

[AArch64] Cleanup logic around aarch64_final_prescan

	* config/aarch64/aarch64.h (ADJUST_INSN_LENGTH): Wrap definition in
	do while (0).
	* config/aarch64/aarch64.c (is_mem_p): Delete.
	(is_memory_op): Rename to...
	(has_memory_op): ... This.  Use FOR_EACH_SUBRTX.
	(dep_between_memop_and_curr): Assert that the input is a SET.
	(aarch64_madd_needs_nop): Add comment.  Do not call
	dep_between_memop_and_curr on NULL body.
	(aarch64_final_prescan_insn): Add comment.
	Include rtl-iter.h.

From-SVN: r216637