gma500/cdv: Add eDP support

Introduce the eDP support into the driver.

This has been reworked a bit because kernel driver proper uses encoder/connectors
while the legacy Intel driver uses the old output stuff.

It also diverges on the backlight handling. The legacy Intel driver adds a panel
abstraction based upon the i915 one. It's only really used for backlight bits
and we have a perfectly good backlight abstraction which can extend instead.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
[ported to upstream driver, redid backlight abstraction]
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/gma500/opregion.c

@@ -166,8 +166,7 @@ static u32 asle_set_backlight(struct drm_device *dev, u32 bclp)
 
 	if (config_enabled(CONFIG_BACKLIGHT_CLASS_DEVICE)) {
 		int max = bd->props.max_brightness;
-		bd->props.brightness = bclp * max / 255;
-		backlight_update_status(bd);
+		gma_backlight_set(dev, bclp * max / 255);
 	}
 
 	asle->cblv = (bclp * 0x64) / 0xff | ASLE_CBLV_VALID;