iwlwifi: mvm: don't disable power management due to P2P device

Currently power management is supported only when only a single
virtual interface is present. The driver verifies number of created
interfaces and disables power management when multiple interfaces
present. However, this rule does not extend to a P2P device that is
handled differently in the firmware. If a P2P device is added power
management can remain enabled.

Signed-off-by: Alexander Bondar <alexander.bondar@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>