ARM: Kirkwood: Use fixed-regulator instead of board gpio call

With the change to a DT based pinctrl/gpio driver, using gpio API
calls in board-*.c files no longer works, a dereferenced NULL pointer
exception occurs instead. By converting the GPIO code into a
fixed-regulator which gets probed later once pinctrl/gpio is
available, we avoid the exception.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Stefan Peter <s.peter@mplch>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>