P2P support was added to the wpa_supplicant D-Bus interface long time
ago, but there has been no attempt of documenting that interface so far.
This commit adds at least a list of new interfaces, methods, properties,
and signals. Some of the incorrect and/or strange parts of the interface
are also identified with bug/todo comments.
Signed-off-by: Jouni Malinen <j@w1.fi>