video: da8xx-fb: use devres

Replace existing resource handling in the driver with managed device
resource.

v2: implement some changes as recommended by
	Prabhakar Lad <prabhakar.csengg@gmail.com>

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Darren Etheridge <detheridge@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>