mpeg2vldemo is the only file requiring cxx support. It is not needed for
buildroot, so disable its compilation to avoid depending on cxx.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>

diff -uNr libva-1.3.0.org/test/Makefile.am libva-1.3.0/test/Makefile.am
--- libva-1.3.0.org/test/Makefile.am	2014-03-24 05:49:46.000000000 +0100
+++ libva-1.3.0/test/Makefile.am	2014-04-26 18:12:25.644390292 +0200
@@ -20,7 +20,7 @@
 # TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 # SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
-SUBDIRS = common decode encode vainfo
+SUBDIRS = common encode vainfo
 
 if USE_X11
 SUBDIRS += basic putsurface