OMAPDSS: add dss_get_core_pdev()

Add dss_get_core_pdev() which returns the platform device for dss core
device. The following patches use the core pdev to register sysfs files
in the compat code.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
diff --git a/drivers/video/omap2/dss/dss.h b/drivers/video/omap2/dss/dss.h
index 6c3cfb3..9ee3c88 100644
--- a/drivers/video/omap2/dss/dss.h
+++ b/drivers/video/omap2/dss/dss.h
@@ -160,6 +160,7 @@
 struct platform_device;
 
 /* core */
+struct platform_device *dss_get_core_pdev(void);
 struct bus_type *dss_get_bus(void);
 struct regulator *dss_get_vdds_dsi(void);
 struct regulator *dss_get_vdds_sdi(void);