Enable VA-API support.

Index: m4/video_out.m4
--- m4/video_out.m4.orig
+++ m4/video_out.m4
@@ -49,6 +49,10 @@ AC_DEFUN([XINE_VIDEO_OUT_PLUGINS], [
             default_enable_vaapi=yes
             ;;
 
+        openbsd*)
+            default_enable_vaapi=yes
+            ;;
+
         gnu*)
             default_enable_vdpau=yes
             ;;
