avutil/internal.h: add timer.h back

Without this a developer would have to add a include every time he
wants to benchmark some code, this is a moderate inconvenience.

This reverts the specific hunk from fb0c9d41d6

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/internal.h

@@ -36,6 +36,7 @@
 #include <assert.h>
 #include "config.h"
 #include "attributes.h"
+#include "timer.h"
 #include "cpu.h"
 #include "dict.h"
 #include "version.h"