iwlwifi: support version 5 of the alive notification

Add support for the new version of the alive notification, which
includes the SKU ID.  We don't use the SKU ID yet, so we can just
handle the new notification as if it were version 4.

While at it, clean up a bit and rename the command and structure names
in the comments so that they are aligned with the ones used in the FW.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200930191738.6024b149e9e2.Ifcadb506e994ec352e9ce54399719926bc1bb7ee@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>