sunxi: gpio: introduce compatible for H616

H616 pinctrl is no different configuration wise than others, so just add
compatible for it.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>