aarch64: Cost comparisons embedded in COND_EXPRs

aarch64: Cost comparisons embedded in COND_EXPRs

So far the costing of COND_EXPRs hasn't distinguished between
cases in which the condition is calculated separately or is
built into the COND_EXPR itself.  This patch adds the cost
of any embedded comparison.

Like with the previous patches, this one only becomes active if
a CPU selects use_new_vector_costs.  It should therefore have
a very low impact on other CPUs.

gcc/
	* config/aarch64/aarch64.c (aarch64_embedded_comparison_type): New
	function.
	(aarch64_adjust_stmt_cost): Add the costs of embedded scalar and
	vector comparisons.