vect: Move vector costs to loop_vec_info

vect: Move vector costs to loop_vec_info

target_cost_data is in vec_info but is really specific to
loop_vec_info.  This patch moves it there and renames it to
vector_costs, to distinguish it from scalar target costs.

gcc/
	* tree-vectorizer.h (vec_info::target_cost_data): Replace with...
	(_loop_vec_info::vector_costs): ...this.
	(LOOP_VINFO_TARGET_COST_DATA): Delete.
	* tree-vectorizer.c (vec_info::vec_info): Remove target_cost_data
	initialization.
	(vec_info::~vec_info): Remove corresponding delete.
	* tree-vect-loop.c (_loop_vec_info::_loop_vec_info): Initialize
	vector_costs to null.
	(_loop_vec_info::~_loop_vec_info): Delete vector_costs.
	(vect_analyze_loop_operations): Update after above changes.
	(vect_analyze_loop_2): Likewise.
	(vect_estimate_min_profitable_iters): Likewise.
	* tree-vect-slp.c (vect_slp_analyze_operations): Likewise.