avcodec/utvideodec: use cached bitstream reader everywhere except on x86_32

From 100x real-time decoding to 138x real-time decoding for 320x240 video.
Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavcodec/utvideodec.c

@@ -27,6 +27,7 @@
 #include <inttypes.h>
 #include <stdlib.h>
 
+#define CACHED_BITSTREAM_READER !ARCH_X86_32
 #define UNCHECKED_BITSTREAM_READER 1
 
 #include "libavutil/intreadwrite.h"