mac80211: allow driver to generate P1K for IV32

In order to support pre-populating the P1K cache in
iwlwifi hardware for WoWLAN, we need to calculate
the P1K for the current IV32. Allow drivers to get
the P1K for any given IV32 instead of for a given
packet, but keep the packet-based version around as
an inline.

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