iwlwifi: mvm: Add device wide power command

FW starts using legacy power table command (0x77) for device wide power
settings. Currently this command contains only option flags field.
It can configure the following: CAM (Continuous Active Mode) and
POWER_SAVE_ENABLE debug option. Send this command when firmware is
loaded - D0 and D3.
Note: Setting this command is important to avoid unwanted FW behavior.
It particularly fixes a bug when a device does not drop to low power
after disassociation from AP.

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>