greybus: control: drop legacy-protocol dependency

Drop dependency on the legacy protocol abstraction.

Instead implement the protocol-specific version request directly, and
use the new interface for managing the control connection.

Note that the version request is being removed from most protocols, but
we need to keep the current request for the control protocol as-is
indefinitely to maintain backwards compatibility (e.g. with the ES2/ES3
bootrom).

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