mwl8k: Enable HW encryption for AP mode

set_key callback is defined for mac80211 to install keys for HW crypto in AP
mode. Driver currently falls back to SW crypto in STA mode.  Add support to
configure the keys appropriately in the hardware after the set_key routine is
called.

Signed-off-by: Nishant Sarmukadam <nishants@marvell.com>
Signed-off-by: Pradeep Nemavat <pnemavat@marvell.com>
Signed-off-by: Thomas Pedersen <thomas@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>