greybus: vibrator-gb: move vibrator protocol to a stand-alone module.

We can't use the gb_protocol_driver() macro here as we need to do some
init and exit logic when loading and removing, so "open code" the module
init and exit functions.

Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
Reviewed-by: Alex Elder <elder@linaro.org>