lavu: extend size of the AVPixFmtDescriptor.flags field

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

doc/APIchanges

@@ -13,6 +13,9 @@ libavutil:     2015-08-28
 
 API changes, most recent first:
 
+2015-xx-xx - lavu 55.0.0
+  xxxxxxx - Change type of AVPixFmtDescriptor.flags from uint8_t to uint64_t.
+
 2015-xx-xx - lavu 54.17.0
   xxxxxxx -  Add av_blowfish_alloc().
   xxxxxxx -  Add av_rc4_alloc().

libavutil/pixdesc.h

@@ -87,7 +87,11 @@ typedef struct AVPixFmtDescriptor {
      * This value only refers to the chroma components.
      */
     uint8_t log2_chroma_h;
-    uint8_t flags;
+
+    /**
+     * Combination of AV_PIX_FMT_FLAG_... flags.
+     */
+    uint64_t flags;
 
     /**
      * Parameters that describe how pixels are packed. If the format