configure: tell user if libva is enabled like the rest of external libs.

Signed-off-by: Anton Khirnov <anton@khirnov.net>

configure

@@ -3131,6 +3131,7 @@ echo "librtmp enabled           ${librtmp-no}"
 echo "libschroedinger enabled   ${libschroedinger-no}"
 echo "libspeex enabled          ${libspeex-no}"
 echo "libtheora enabled         ${libtheora-no}"
+echo "libva enabled             ${vaapi-no}"
 echo "libvorbis enabled         ${libvorbis-no}"
 echo "libvpx enabled            ${libvpx-no}"
 echo "libx264 enabled           ${libx264-no}"