drm/i915: Don't enable backlight at setup time.

drm/i915: Don't enable backlight at setup time.

Maarten and Ville noticed that we are enabling backlight via DP aux very
early in the modeset_init path via the intel_dp_aux_setup_backlight()
function, since commit e7156c833903 ("drm/i915: Add Backlight Control using
DPCD for eDP connectors (v9)"). Looks like all we need to do during
_setup_backlight() is read the current brightness state instead of
modifying it.

v2: Rewrote commit message.

Cc: Ville Syrjala <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Yetunde Adebisi <[email protected]>
Signed-off-by: Dhinakaran Pandiyan <[email protected]>
Reviewed-by: Maarten Lankhorst <[email protected]>
Acked-by: Jani Nikula <[email protected]>
Tested-by: Puthikorn Voravootivat <[email protected]>
Fixes: e7156c833903 ("drm/i915: Add Backlight Control using DPCD for eDP connectors (v9)")
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Ville Syrjälä <[email protected]>