cfg80211: Add feature flag for Fast Initial Link Setup (FILS) as STA

This defines a feature flag that drivers can use to indicate that they
support FILS authentication/association (IEEE 802.11ai) when using user
space SME (NL80211_CMD_AUTHENTICATE) in station mode.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>