[ARM] pxa/em-x270: don't use pxa_camera init() callback

pxa_camera init() is ambiguous, it's better to statically configure the sensor.

Signed-off-by: Antonio Ospite <ospite@studenti.unina.it>
Acked-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>