ath9k/carl9170: advertise P2P

With some upcoming changes we'd like to use
the interface types for P2P capability tests.
Enable them now so that when we add those
tests in wpa_supplicant, nothing will break.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>