ap: add support for the AP Device ID unipro management function message

The AP needs to know its assigned Device ID in order to establish
Greybus connections between CPorts. We could have pulled the Device
ID from the controller hardware in a driver specific manner, but
instead we define one generic message from the SVC to let the
AP know this information. Add this additional unipro management
message and handle it by setting the supplied Device ID in the
struct greybus_host_device. The greybus core will use this to
populate the source Device ID when establishing a connection
between the AP and another module's CPort.

Signed-off-by: Matt Porter <mporter@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>