sh-pfc: r8a73a4: Remove function GPIOs

All r8a73a4 platforms use the pinctrl API to control pin functions.
Function GPIOs are no longer needed.

Signed-off-by: Magnus Damm <damm@opensource.se>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>