cfg80211: use separate struct for FILS parameters

Put FILS related parameters into their own struct definition so
it can be reused for roam events in subsequent change.

Reviewed-by: Jithu Jance <jithu.jance@broadcom.com>
Reviewed-by: Eylon Pedinovsky <eylon.pedinovsky@broadcom.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>