iwlwifi: move iwl_cfg from iwl_priv to iwl_shared

Move the configuration pointer from the upper level iwl_priv to the
lower level iwl_shared structure, with associated code fixes.

Signed-off-by: Don Fry <donald.h.fry@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>