[media] mt9m111: properly implement .s_crop and .s_fmt(), reset on STREAMON

mt9m111 camera sensors support cropping and scaling. The current
implementation is broken. For example, .s_crop() sets output frame sizes
instead of the input cropping window. This patch adds a proper implementation
of these methods. Besides it adds a sensor-disable and -enable operations
on first open() and last close() respectively, to save power while closed and
to return the camera to the default power-on state.

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