compositor: Support notifying with absolute position too

With evdev input devices that generate absolute positions we need to provide
an infrastructure in the compositor for supporting those.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=61997
diff --git a/src/compositor.h b/src/compositor.h
index 4cc24d8..dc03aeb 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -556,7 +556,10 @@
 			struct weston_seat *seat);
 void
 notify_motion(struct weston_seat *seat, uint32_t time,
-	      wl_fixed_t x, wl_fixed_t y);
+	      wl_fixed_t dx, wl_fixed_t dy);
+void
+notify_motion_absolute(struct weston_seat *seat, uint32_t time,
+		       wl_fixed_t x, wl_fixed_t y);
 void
 notify_button(struct weston_seat *seat, uint32_t time, int32_t button,
 	      enum wl_pointer_button_state state);