drm/i915/bxt: set min brightness from VBT

Min brightness value from vbt was missing for BXT platform.
This setting have to refer backlight ic spec to restrict
min backlight output. Without this restriction, driver would
allow to configure lower brightness value and violate
backlight ic requirement.

Fixes: 0fb890c ("drm/i915/bxt: BLC implementation")
Cc: Jani Nikula <[email protected]>
Cc: Cooper Chiou <[email protected]>
Cc: Gary C Wang <[email protected]>
Signed-off-by: Shawn Lee <[email protected]>
Signed-off-by: Jani Nikula <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit c388112)
Signed-off-by: Rodrigo Vivi <[email protected]>

drivers/gpu/drm/i915/intel_panel.c

@@ -1699,6 +1699,8 @@ bxt_setup_backlight(struct intel_connector *connector, enum pipe unused)
 	if (!panel->backlight.max)
 		return -ENODEV;
 
+	panel->backlight.min = get_backlight_min_vbt(connector);
+
 	val = bxt_get_backlight(connector);
 	val = intel_panel_compute_brightness(connector, val);
 	panel->backlight.level = clamp(val, panel->backlight.min,