ivi-shell: add interface to get screen ID

This interface is required for user to manage screens per IDs.

Signed-off-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@xddp.denso.co.jp>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
diff --git a/ivi-shell/ivi-layout-export.h b/ivi-shell/ivi-layout-export.h
index 2f93811..68d3760 100644
--- a/ivi-shell/ivi-layout-export.h
+++ b/ivi-shell/ivi-layout-export.h
@@ -797,6 +797,13 @@
 						      layer_property_notification_func callback,
 						      void *userdata);
 
+	/**
+	 * \brief get id of ivi_screen from ivi_layout_screen
+	 *
+	 *
+	 * \return id of ivi_screen
+	 */
+	uint32_t (*get_id_of_screen)(struct ivi_layout_screen *iviscrn);
 };
 
 #ifdef __cplusplus