The frontbuffer code gives us accurate information about activity,
let's use it. Again this should avoid unecessary updates when multiple
screens are on.

Also realign function paramaters, I couldn't resist that bit of OCD.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Durgadoss R <durgadoss.r@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>