drm/rcar-du: Rename rcar_du_plane_(init|register) to rcar_du_planes_*

The functions initialize or register all planes, rename them
accordingly.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

diff --cc drivers/gpu/drm/rcar-du/rcar_du_kms.c
Simple merge

diff --cc drivers/gpu/drm/rcar-du/rcar_du_plane.c
Simple merge

diff --cc drivers/gpu/drm/rcar-du/rcar_du_plane.h
Simple merge