ARM: shmobile: r8a7790: Remove all GPIOs

Function GPIOs are not used anymore, and all code use the GPIO numbers
directly. Remove the GPIOs enumeration.
Signed-off-by: NLaurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>