pinctrl: sh-pfc: r8a7791: Split the DU sync and cde/disp groups

The DU parallel interface ODDF signal is optional, move it out of the
HSYNC/VSYNC group into a group of its down. The CDE and DISP signals are
independent, split them to two different groups.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>