iwlwifi: replace d0i3_mode and wowlan_d0i3 with more generic variables

iwlwifi: replace d0i3_mode and wowlan_d0i3 with more generic variables

The d0i3_mode variable is used to distinguish between transports that
handle d0i3 entry during suspend by themselves (i.e. the slave
transports) and those which rely on the op_mode layer to do it.  The
reason why the former do it by themselves is that they need to
transition from d0i3 in runtime_suspend into d0i3 in system-wide
suspend and this transition needs to happen before the op_mode's
suspend flow is called.

The wowlan_d0i3 element is also a bit confusing, because it just
reflects the wowlan->any value for the trans to understand.  This is a
bit unclear in the code and not generic enough for future use.

To make it clearer and to generalize the platform power mode settings,
introduce two variables to indicate the platform power management
modes used by the transport.

Additionally, in order not to take too big a step in one patch, treat
this new variables semantically in the same way as the old d0i3_mode
element, introducing a iwl_mvm_enter_d0i3_on_suspend() function to
help with that.

This commit also adds the foundation for a new concept where the
firmware configuration state (i.e. D0, D3 or D0i3) is abstracted from
the platform PM mode we are in (i.e. runtime suspend or system-wide
suspend).

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>