ARM: Dove: Add CuBox pinhog for led

SolidRun CuBox has a led on a gpio pin. As there is now DT pinctrl
support for Dove, make use of a pinhog to ensure the pin is set to
gpio.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>