Include config.h to have VA_DRIVER_INIT_FUNC

The VA_DRIVER_INIT_FUNC macro is defined by configure in config.h, if
this header is not included then the init symbol will not be present and
libVA will not be able to load this backend.

src/sunxi_cedrus_drv_video.c

@@ -31,6 +31,8 @@
 #include "surface.h"
 #include "va_config.h"
 
+#include "config.h"
+
 #include <va/va_backend.h>
 
 #include "sunxi_cedrus_drv_video.h"