VECT: Apply LEN_MASK_{LOAD,STORE} into vectorizer

VECT: Apply LEN_MASK_{LOAD,STORE} into vectorizer

Address comments from Richard and Bernhard from V5 patch.
V6 fixed all issues according their comments.

gcc/ChangeLog:

	* internal-fn.cc (expand_partial_store_optab_fn): Adapt for LEN_MASK_STORE.
	(internal_load_fn_p): Add LEN_MASK_LOAD.
	(internal_store_fn_p): Add LEN_MASK_STORE.
	(internal_fn_mask_index): Add LEN_MASK_{LOAD,STORE}.
	(internal_fn_stored_value_index): Add LEN_MASK_STORE.
	(internal_len_load_store_bias):  Add LEN_MASK_{LOAD,STORE}.
	* optabs-tree.cc (can_vec_mask_load_store_p): Adapt for LEN_MASK_{LOAD,STORE}.
	(get_len_load_store_mode): Ditto.
	* optabs-tree.h (can_vec_mask_load_store_p): Ditto.
	(get_len_load_store_mode): Ditto.
	* tree-vect-stmts.cc (check_load_store_for_partial_vectors): Ditto.
	(get_all_ones_mask): New function.
	(vectorizable_store): Apply LEN_MASK_{LOAD,STORE} into vectorizer.
	(vectorizable_load): Ditto.