video: imxfb: Convert to SIMPLE_DEV_PM_OPS

Instead of assigning the pm_ops fields individually we can simply
use SIMPLE_DEV_PM_OPS.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>