V4L/DVB (10090): soc-camera: let drivers decide upon supported field values

sh_mobile_ceu_camera.c is already prepared to support interlaced format, this
patch moves the choice of a field type down to host and / or camera drivers.

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