iwlwifi: fix device id registration for 6000 series 2x2 devices

Add device ids for 2x2 devices. Also fix antenna usage because these devices use
antennas A and B, not B and C.

Signed-off-by: Jay Sternberg <jay.e.sternberg@linux.intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>