Apply TLC to vect_supportable_dr_alignment

Apply TLC to vect_supportable_dr_alignment

This fixes handling of the return value of vect_supportable_dr_alignment
in multiple places.  We should use the enum type and not int for
storage and not auto-convert the enum return value to bool.  It also
commonizes the read/write path in vect_supportable_dr_alignment.

2021-10-18  Richard Biener  <rguenther@suse.de>

	* tree-vect-data-refs.c (vect_peeling_hash_insert): Do
	not auto-convert dr_alignment_support to bool.
	(vect_peeling_supportable): Likewise.
	(vect_enhance_data_refs_alignment): Likewise.
	(vect_supportable_dr_alignment): Commonize read/write case.
	* tree-vect-stmts.c (vect_get_store_cost): Use
	dr_alignment_support, not int, for the vect_supportable_dr_alignment
	result.
	(vect_get_load_cost): Likewise.