Support for P4 devices is now available via P4 RuntimeP4Runtime.Check this page for more information.
The content of this page is deprecated. Support for BMv2 and P4 as described here won't be available anymore starting from ONOS 1.11 (Loon). Instead, the recently started P4 Brigade is working on official support for P4-enabled devices via P4Runtime. Please subscribe to the brigade's mailing list to receive updates.
If you still want to to try the P4 support as described on this page please make sure to use ONOS 1.6 (Goldeneye).