greybus: interface: read DME attributes at activation

Read the DDBL1 and Ara DME attributes when activating an interface.

These values are currently provided by the SVC in the intf_hotplug
request, which is about to go away.

Note that there are currently no standard Ara VID and PID attributes and
that Toshiba uses attributes from the reserved space in ES3. For now, we
therefore refuse to enumerate any non-Toshiba bridges.

Also note that the Ara serial number is currently not supported.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>