sh-pfc: r8a7779: Remove function GPIOs

All r8a7779 platforms use the pinctrl API to control functions. Function
GPIOs are unused and unneeded, remove them.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>