Use helper function to set input in v4l2 input.
Use helper function to set format in v4l2 input.

Since the helper function also needs to pack/unpack the resolution, the
pack/unpack functions were moved to the helper library and prefixed with
v4l2_ in order to avoid possible collisions.
Use helper function to set framerate in v4l2 input.
Add option to leave settings unchanged in v4l2 input.

This adds an additional option for all settings to leave the current
configuration of the device unchanged.