sh-pfc: r8a7790: Remove function GPIOs

No r8a7770 platform use the function GPIOs API. Remove it.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
[horms+renesas@verge.net.au: fixed typo in changelog: r8a7779 -> r8a7770]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>