ARM: shmobile: r8a73a4: Remove all GPIO enums

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