iwlwifi: mvm: stop using DEVICE_POWER_FLAGS_CAM_MSK

The firmware has always treated these two bits to mean that
powersave is enabled when POWER_SAVE_ENA is set and CAM is
clear; it doesn't use them in any non-combined way.

Therefore, it's pointless to send it two bits, and the API
should be cleaned up. Prepare the driver by removing the CAM
bit and using only POWER_SAVE_ENA to indicate whether PS is
enabled or not.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>