compositor-drm: add DPI connector type

Linux v4.7 introduced a new connector type for display parallel
interface (DPI). Add DPI to the list of connectors in the DRM
backend of Weston as well. This avoid DPI connectors showing up
as UNNAMED.

Signed-off-by: Stefan Agner <stefan@agner.ch>
diff --git a/libweston/compositor-drm.c b/libweston/compositor-drm.c
index 70e966c..3891176 100644
--- a/libweston/compositor-drm.c
+++ b/libweston/compositor-drm.c
@@ -4549,6 +4549,9 @@
 	[DRM_MODE_CONNECTOR_VIRTUAL]     = "Virtual",
 	[DRM_MODE_CONNECTOR_DSI]         = "DSI",
 #endif
+#ifdef DRM_MODE_CONNECTOR_DPI
+	[DRM_MODE_CONNECTOR_DPI]         = "DPI",
+#endif
 };
 
 /** Create a name given a DRM connector