modules/codec/avcodec: Move HAVE_AVCODEC_MT to avcodec.h

The defined HAVE_AVCODEC_MT is used by modules/codec/avcodec/avcodec.c
and modules/codec/avcodec/video.c. It was only defined in modules/codec/avcodec/video.c.

This patch moves the define to modules/codec/avcodec/avcodec.h.

modules/codec/avcodec/avcodec.h

@@ -268,6 +268,10 @@ int ffmpeg_OpenCodec( decoder_t *p_dec );
 #   define AV_VERSION_INT(a, b, c) ((a)<<16 | (b)<<8 | (c))
 #endif
 
+#if defined(FF_THREAD_FRAME)
+#   define HAVE_AVCODEC_MT
+#endif
+
 /* Uncomment it to enable compilation with vaapi/dxva2 (you also must change the build
  * system) */
 //#define HAVE_AVCODEC_VAAPI 1

modules/codec/avcodec/video.c

@@ -55,9 +55,6 @@
 #if defined(HAVE_AVCODEC_VAAPI) || defined(HAVE_AVCODEC_DXVA2)
 #   define HAVE_AVCODEC_VA
 #endif
-#if defined(FF_THREAD_FRAME)
-#   define HAVE_AVCODEC_MT
-#endif
 
 /*****************************************************************************
  * decoder_sys_t : decoder descriptor