iwlwifi: mvm: Handle power management constraints for additional use-cases

Today, the driver logic looks for the conditions to disable
power management albeit power management should be enabled
in a very few distinct cases.
This patch changes the driver logic to enable power
management once the required conditions met.
While at it, make some housekeeping and support a few
additional use cases:

a) Add support for a standalone p2p client:
   Power management should be enabled for a P2P client
   MAC only if the firmware supports it (TLV flag is set).
   Instead we used the DCM flag, therefore we didn't cover
   use cases that did not include the DCM flag.

b) Add support to Same-Channel-Mode (SCM):
   If both clients share the same channel (SCM), and there
   are no other active vifs in the system, power management
   should be enabled only if the firmware supports this
   (TLV flag is set).

c) Fix power management logic for GO/AP:
   Today, when we detect an active GO / AP MAC - we disable
   power management for all the vifs altogether.
   Actually, the correct behavior is to enable power
   management on a client if on a different channel
   (based on the firmware capabilities).

d) Housekeeping - Along with that, this patch includes some
   code-reorganizing: Today the logic of disabling power is
   scattered across several functions, specifically in the
   iterator. For the sake of both readability and
   scalability, we moved this logic to its applicable
   function, leaving the iterator gather information only.
   Furthermore, as power management is a MAC-related
   attribute, we moved the power management member to the
   iwl_mvm_vif structure.

Signed-off-by: Avri Altman <avri.altman@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>