avcodec/vdpau.h: define FF_API_CAP_VDPAU if its not defined

Prevent build failure for applicatins using the old API
This could be replaced be a include of version.h but some applications
would then need extern C wrapers
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/vdpau.h

@@ -53,6 +53,10 @@
 #include <vdpau/vdpau_x11.h>
 #include "libavutil/avconfig.h"
 
+#ifndef FF_API_CAP_VDPAU
+#define FF_API_CAP_VDPAU 1
+#endif
+
 union AVVDPAUPictureInfo {
     VdpPictureInfoH264        h264;
     VdpPictureInfoMPEG1Or2    mpeg;