cfg80211: support 4-way handshake offloading for 802.1X

Add API for setting the PMK to the driver. For FT support, allow
setting also the PMK-R0 Name.

This can be used by drivers that support 4-Way handshake offload
while IEEE802.1X authentication is managed by upper layers.

Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
[arend.vanspriel@broadcom.com: add WANT_1X_4WAY_HS attribute]
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
[reword NL80211_EXT_FEATURE_4WAY_HANDSHAKE_STA_1X docs a bit to
say that the device may require it]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>