greybus: camera: HACK: Register gb camera to the HOST camera

This change implements gb camera interface and register
gb camera to the HOST driver.
This implementation need to be reworked after the demo.

Tested with db3 with two camera modules.

Signed-off-by: Gjorgji Rosikopulos <grosikopulos@mm-sol.com>
Acked-by: Laurent Pinchart <laurent.pinchart@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>