avutil/reverse: move the ff_reverse declaration to a separate header

Fixes compilation with hardcoded tables after eaff1aa09e
and e71b8119e7

Reviewed-by: Timo Rothenpieler <timo@rothenpieler.org>
Signed-off-by: James Almer <jamrial@gmail.com>

libavutil/eval.c

@@ -38,6 +38,7 @@
 #include "time.h"
 #include "avstring.h"
 #include "timer.h"
+#include "reverse.h"
 
 typedef struct Parser {
     const AVClass *class;