vect: Remove non-SLP path from vectorizable_reduction

vect: Remove non-SLP path from vectorizable_reduction

Fold slp_node to TRUE and clean-up vectorizable_reduction and related functions.
Also split up vectorizable_lc_phi and create vect_transform_lc_phi.

gcc/ChangeLog:

	* tree-vect-loop.cc (get_initial_def_for_reduction): Remove.
	(vect-create_epilog_for_reduction): Remove non-SLP path.
	(vectorize_fold_left_reduction): Likewise.
	(vectorizable_lane_reducing): Likewise.
	(vectorizable_reduction): Likewise.
	(vect_transform_reduction): Likewise.
	(vect_transform_cycle_phi): Likewise.
	(vectorizable_lc_phi): Remove non-SLP PATH and split into...
	(vect_transform_lc_phi): ... this.
	(update_epilogue_loop_vinfo): Update comment.
	* tree-vect-stmts.cc (vect_analyze_stmt): Update call to
	vectorizable_lc_phi.
	(vect_transform_stmt): Update calls to vect_transform_reduction and
	vect_transform_cycle_phi.  Rename call from vectorizable_lc_phi to
	vect_transform_lc_phi.
	* tree-vectorizer.h (vect_transform_reduction): Update declaration.
	(vect_transform_cycle_phi): Likewise.
	(vectorizable_lc_phi): Likewise.
	(vect_transform_lc_phi): New.