drm/i915: switch off backlight for backlight class 0 brightness
drm/i915: switch off backlight for backlight class 0 brightness

Make backlight class sysfs brightness 0 value switch off the backlight
for connectors that have the backlight_power callback defined. For eDP,
this has the similar caveats regarding power savings as bl_power as only
the power sequencer backlight control is switched off.

Signed-off-by: Jani Nikula <ba783f3beccaedfda693f41a15407d612a629408@intel.com>
Reviewed_by: Clinton Taylor <Clinton.A.Taylor@intel.com>
Signed-off-by: Daniel Vetter <c1b6782c4af8f0673da8923a0702a1832e5940f4@ffwll.ch>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs