Move opt_loglevel() from ffmpeg.c to cmdutils.c.

Originally committed as revision 19209 to svn://svn.ffmpeg.org/ffmpeg/trunk

cmdutils.h

@@ -50,6 +50,11 @@ extern struct SwsContext *sws_opts;
  */
 int opt_default(const char *opt, const char *arg);
 
+/**
+ * Sets the libav* libraries log level.
+ */
+int opt_loglevel(const char *opt, const char *arg);
+
 /**
  * Parses a string and returns its corresponding value as a double.
  * Exits from the application if the string cannot be correctly