configure.ac: Auto-enable vaapi recorder, but allow overrides

If libva is available and recent, we'll enable the vaapi recorder feature,
but it can also be forced on or off by --enable/disable-vaapi-recorder.
diff --git a/src/compositor-drm.c b/src/compositor-drm.c
index 23d6f0f..4c4b9c6 100644
--- a/src/compositor-drm.c
+++ b/src/compositor-drm.c
@@ -2446,7 +2446,7 @@
 	}
 }
 
-#ifdef HAVE_LIBVA
+#ifdef BUILD_VAAPI_RECORDER
 static void
 recorder_frame_notify(struct wl_listener *listener, void *data)
 {