sh-pfc: r8a7740: Remove FSI function GPIOS

All r8a7740 platforms now use the pinctrl API to control the FSI pins,
the corresponding function GPIOS are unused. Remove them.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>