sh-pfc: r8a7779: Remove DU1_DOTCLKOUT1 GPIO

The function is not documented in the r8a7779 datasheet. Remove it.

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