iwlwifi: configure power scheme to balanced for 22560 devices

As a temporary stage in the 22560 devices bring up, we disabled
power save, to avoid bugs related to that domain.
Now we would like to use power save so enable the balanced mode,
and allow configuring the mode via module parameter.

Signed-off-by: Golan Ben Ami <golan.ben.ami@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>