Refactor vect_supportable_dr_alignment

Refactor vect_supportable_dr_alignment

This refactors vect_supportable_dr_alignment to get the misalignment
as input parameter which allows us to elide modifying/restoring
of DR_MISALIGNMENT during alignment peeling analysis which eventually
makes it more straight-forward to split out the negative step
handling.

2021-10-19  Richard Biener  <rguenther@suse.de>

	* tree-vectorizer.h (vect_supportable_dr_alignment): Add
	misalignment parameter.
	* tree-vect-data-refs.c (vect_get_peeling_costs_all_drs):
	Do not change DR_MISALIGNMENT in place, instead pass the
	adjusted misalignment to vect_supportable_dr_alignment.
	(vect_peeling_supportable): Likewise.
	(vect_peeling_hash_get_lowest_cost): Adjust.
	(vect_enhance_data_refs_alignment): Likewise.
	(vect_vfa_access_size): Likewise.
	(vect_supportable_dr_alignment): Add misalignment
	parameter and simplify.
	* tree-vect-stmts.c (get_negative_load_store_type): Adjust.
	(get_group_load_store_type): Likewise.
	(get_load_store_type): Likewise.