phdc: Initial PHDC implementation

phdc: Initial PHDC implementation

Code to add the PHDC p2p driver. This driver will publish a dbus
interface to facilitate PHDC Managers registration. This code handles
multiple Managers.

Managers (or Agents) should register using RegisterAgent(), and should
publish a specific interface "org.neard.PHDC.Manager" or
"org.neard.PHDC.Agent".
PHDC is different from usual p2p services as it is a proprietary
service. The PHDC Manager (external to neard) notify neard for being
registered on specific services urn (e.g: urn:nfc:sn:phdc)
The PHDC Agent connects to this specific urn using p2p, and the newly
created p2p file descriptor is forwarded to the PHDC Manager.
Doing this, the PHDC driver acts as a passthru, allowing the Agent to
exchange with the Manager.