P2P: Remove P2P group on driver resource becoming unavailable

P2P: Remove P2P group on driver resource becoming unavailable

Add a new driver event, EVENT_INTERFACE_UNAVAILABLE, for indicating
that the driver is not able to continue operating the virtual
interface in its current mode anymore, e.g., due to operating
channel for GO interface forced to a DFS channel by another virtual
interface.

When this happens for a P2P group interface, the P2P group will
be terminated and P2P-GROUP-REMOVED event shows the reason for
this as follows:
P2P-GROUP-REMOVED wlan0 GO reason=UNAVAILABLE