Include libavutil/channel_layout.h instead of libavutil/audioconvert.h

Also reorder some other #include when applicable.
diff --git a/libavcodec/mpc7.c b/libavcodec/mpc7.c
index b013eeb..7c9103c 100644
--- a/libavcodec/mpc7.c
+++ b/libavcodec/mpc7.c
@@ -25,12 +25,12 @@
  * divided into 32 subbands.
  */
 
+#include "libavutil/channel_layout.h"
 #include "libavutil/lfg.h"
 #include "avcodec.h"
 #include "get_bits.h"
 #include "dsputil.h"
 #include "mpegaudiodsp.h"
-#include "libavutil/audioconvert.h"
 
 #include "mpc.h"
 #include "mpc7data.h"