ffmpeg: add ui64 type to SpecifierOpt

Adds ui64 (uint64_t) as a possible type for SpecifierOpt. This enables
 use of uint64_t options with SpecifierOpt such as channel_layout
 when expressed as a 64 bit channel mask.

Signed-off-by: pkviet <pkv.stream@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

fftools/cmdutils.h

@@ -155,6 +155,7 @@ typedef struct SpecifierOpt {
         uint8_t *str;
         int        i;
         int64_t  i64;
+        uint64_t ui64;
         float      f;
         double   dbl;
     } u;