mmal: Reference MMAL VC lib explicitly

This is optional, but ensures that linking with -Wl,--as-needed does not
drop the library containing the MMAL VC driver. The driver normally
"registers" itself in the library constructor, but since no symbols are
explicitly referenced, the linker could remove it with --as-needed
enabled.
Signed-off-by: Diego Biurrun <diego@biurrun.de>

libavcodec/mmaldec.c

@@ -29,6 +29,7 @@
 #include <interface/mmal/util/mmal_util.h>
 #include <interface/mmal/util/mmal_util_params.h>
 #include <interface/mmal/util/mmal_default_components.h>
+#include <interface/mmal/vc/mmal_vc_api.h>
 
 #include "avcodec.h"
 #include "internal.h"
@@ -182,6 +183,8 @@ static av_cold int ffmmal_close_decoder(AVCodecContext *avctx)
     if (ctx->bsfc)
         av_bitstream_filter_close(ctx->bsfc);
 
+    mmal_vc_deinit();
+
     return 0;
 }
 
@@ -321,6 +324,11 @@ static av_cold int ffmmal_init_decoder(AVCodecContext *avctx)
 
     bcm_host_init();
 
+    if (mmal_vc_init()) {
+        av_log(avctx, AV_LOG_ERROR, "Cannot initialize MMAL VC driver!\n");
+        return AVERROR(ENOSYS);
+    }
+
     if ((ret = ff_get_format(avctx, avctx->codec->pix_fmts)) < 0)
         return ret;