aarch64: Remove vectype from latency tests

aarch64: Remove vectype from latency tests

This patch gets the scalar mode of a reduction operation from the
gimple stmt rather than the vectype.  This makes it more suitable
for use in scalar costs.

gcc/
	* config/aarch64/aarch64.c (aarch64_sve_in_loop_reduction_latency):
	Remove vectype parameter and get floatness from the type of the
	stmt lhs instead.
	(arch64_in_loop_reduction_latency): Likewise.
	(aarch64_detect_vector_stmt_subtype): Update caller.
	(aarch64_vector_costs::count_ops): Likewise.