iwlwifi: mvm: split wowlan handling out of the main suspend function

Take the WoWLAN handling code out of the main suspend function,
dividing it into three parts: get_config (which is used before the
firmware is switched), switch_to_d3 (which handles the rebooting of
the hardware with the D3 firmware) and config (which configures the D3
firmware for WoWLAN operation).  This is necessary to prepare for the
net-detect implementation, which will use only the switch_to_d3 part
of this flow.
Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>