iwlwifi: remove duplicated/unused definition

"IWL_CMD_QUEUE_NUM" is being defined in multiple places and used by all
the devices. move it to iwl-dev.h file and shared by all the devices.

Remove "IWL_CMD_FIFO_NUM", replaced by "IWL49_CMD_FIFO_NUM" and IWL50_CMD_FIFO_NUM"

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>