V4L/DVB (9787): soc-camera: let camera host drivers decide upon pixel format

Pixel format requested by the user is not necessarily the same, as what
a sensor driver provides. There are situations, when a camera host driver
provides the required format, but requires a different format from the
sensor. Further, the list of formats, supported by sensors is pretty static
and can be pretty good described with a constant list of structures. Whereas
decisions, made by camera host drivers to support requested formats can be
quite complex, therefore it is better to let the host driver do the work.

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