[media] V4L: soc-camera: add a livecrop host operation

Add an soc-camera host livecrop operation to implement live zoom. If
a host driver implements it, it should take care to preserve output
frame format, then live crop doesn't break streaming.

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