greybus: interface: move vendor and product strings to control device

The control device is an abstraction of the control connection over
which a greybus manifest is retrieved. As interfaces switch modes (e.g.
after boot-over-unipro) they expose new manifests, which can contain
different vendor and product strings.

Eventually control devices will be deregistered and recreated after an
interface mode switch, while the interface itself remains registered.

Note that only interfaces of type greybus will have control devices.
Specifically, dummy interfaces will not.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>