drm/rcar-du: Add support for DEFR8 register

The R8A7790 DU has a new extended function control register. Support it.

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

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

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

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