V4L/DVB (11027): soc-camera: configure drivers with a default format at probe time

Currently soc-camera doesn't set up any image format without an explicit
S_FMT. According to the API this should be supported, for example,
capture-example.c from v4l2-apps by default doesn't issue an S_FMT. This
patch moves negotiating of available host-camera format translations to
probe() time, and restores the state from the last close() on the next
open(). This is needed for some drivers, which power down or reset
hardware after the last user closes the interface. This patch also has a
nice side-effect of avoiding multiple allocation anf freeing of format
translation tables.

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