V4L/DVB (12528): sh_mobile_ceu_camera: implement host-side image scaling

Use host-side image scaling when the client fails to set the requested format.
We also have to take scaling into account when performing host-side cropping.
Similar to cropping we try to use client-side scaling as much as possible to
preserve bus bandwidth and optimise the frame-rate.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>