drm/panel: simple: Update backlight state property

Some backlight drivers ignore the power property and instead only use
the state property. Fixup the panel driver to set the state property in
addition to the power property.
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/panel/panel-simple.c

@@ -168,6 +168,7 @@ static int panel_simple_disable(struct drm_panel *panel)
 
 	if (p->backlight) {
 		p->backlight->props.power = FB_BLANK_POWERDOWN;
+		p->backlight->props.state |= BL_CORE_FBBLANK;
 		backlight_update_status(p->backlight);
 	}
 
@@ -235,6 +236,7 @@ static int panel_simple_enable(struct drm_panel *panel)
 		msleep(p->desc->delay.enable);
 
 	if (p->backlight) {
+		p->backlight->props.state &= ~BL_CORE_FBBLANK;
 		p->backlight->props.power = FB_BLANK_UNBLANK;
 		backlight_update_status(p->backlight);
 	}