mwl8k: add the commands used for AP firmware initialisation

Add the AP version of the GET_HW_SPEC command, as well as the
SET_HW_SPEC command, for initialising AP firmware.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>