drivers:video:fbdev atmel_lcdfb.c power GPIO registration bug

A list that was intended for storing power control GPIOs was never
initialized correctly or filled. Without these lines of added code
the kernel hangs when trying to access an uninitialized list when a
power control GPIO is registered with the device tree.

Signed-off-by: Michael Welling <mwelling@ieee.org>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>