vect: Rename things related to rgroup_masks

vect: Rename things related to rgroup_masks

Power supports vector memory access with length (in bytes) instructions.
Like existing fully masking for SVE, it is another approach to vectorize
the loop using partially-populated vectors.

As Richard Sandiford pointed out, we can rename the rgroup struct
rgroup_masks to rgroup_controls, rename its members mask_type to type,
masks to controls to be more generic.

Besides, this patch also renames some functions like vect_set_loop_mask
to vect_set_loop_control, release_vec_loop_masks to
release_vec_loop_controls, vect_set_loop_masks_directly to
vect_set_loop_controls_directly.

Bootstrapped/regtested on aarch64-linux-gnu.

gcc/ChangeLog:

	* tree-vect-loop-manip.c (vect_set_loop_mask): Renamed to ...
	(vect_set_loop_control): ... this.
	(vect_maybe_permute_loop_masks): Rename rgroup_masks related things.
	(vect_set_loop_masks_directly): Renamed to ...
	(vect_set_loop_controls_directly): ... this.  Also rename some
	variables with ctrl instead of mask.  Rename vect_set_loop_mask to
	vect_set_loop_control.
	(vect_set_loop_condition_masked): Rename rgroup_masks related things.
	Also rename some variables with ctrl instead of mask.
	* tree-vect-loop.c (release_vec_loop_masks): Renamed to ...
	(release_vec_loop_controls): ... this.  Rename rgroup_masks related
	things.
	(_loop_vec_info::~_loop_vec_info): Rename release_vec_loop_masks to
	release_vec_loop_controls.
	(can_produce_all_loop_masks_p): Rename rgroup_masks related things.
	(vect_get_max_nscalars_per_iter): Likewise.
	(vect_estimate_min_profitable_iters): Likewise.
	(vect_record_loop_mask): Likewise.
	(vect_get_loop_mask): Likewise.
	* tree-vectorizer.h (struct rgroup_masks): Renamed to ...
	(struct rgroup_controls): ... this.  Also rename mask_type
	to type and rename masks to controls.