greybus: audio: Allocate protocol and class values

Allocate protocol and class values for the Audio Device Class
Protocol.  Two values of each type are allocated: one for Audio
Management Connections and one for Audio Data Connections.

Signed-off-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>