video: atmel_lcdfb: ensure the hardware is initialized with the correct mode

If no driver takeover the atmel_lcdfb, the lcd won't be in a working state
since atmel_lcdfb_set_par() will never be called. Enabling a driver which does,
like fbcon, will call the function and put atmel_lcdfb in a working state.

Fixes: b985172b (video: atmel_lcdfb: add device tree suport)

Signed-off-by: Antoine Ténart <antoine.tenart@free-electrons.com>
Reported-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>