iwlwifi: refactor testmode

Create an object that will enacpsulate the testmode functionality
that is common to all op modes.

 * Copy definitions from dvm/dev.h
 * Copy the testmode logic from dvm/testmode.c
 * Link iwl-test object into the iwlwifi module
 * Modify DVM to use iwl-test object

Reviewed-by: Amit Beka <amit.beka@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>