input: Provide microsecond timestamps in motion events

Provide timestamps with microsecond granularity if the backend can
provide it. Backends that can't should set it to 0.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
diff --git a/libweston/compositor.h b/libweston/compositor.h
index 29cc8df..45af3e6 100644
--- a/libweston/compositor.h
+++ b/libweston/compositor.h
@@ -248,6 +248,7 @@
 
 struct weston_pointer_motion_event {
 	uint32_t mask;
+	uint64_t time_usec;
 	double x;
 	double y;
 	double dx;