iwlwifi: pcie: separate between SW and HW MSIX configuration

The MSIX configuration flow includes two different stages:
configuring the HW by writing to the IVAR table and configuring the SW
to reflect the HW configuration.
The HW configuration is needed on each HW reset,
whereas the SW configuration is only needed during the init flow.

Signed-off-by: Haim Dreyfuss <haim.dreyfuss@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>