SWSCALE: Increase maximim with from 5120 to 21504

Heres a benchmark

VOFW 5120  VOFW 21504    Note
10438.8    10344.2       timex ffmpeg -y -i tulip2.mp4 tulip2.yuv
25611.9    24256.9       timex ffmpeg -y -itulip2.mp4 -s 1272x724 tulip2.yuv
24485.7    26006.6
28573.1    24291.3
24069.1    26995.9
25684.95   25387.675     average

This is on a Nehalem i7.  Despite being a 500 frame, 720p video, the numbers
fluctuate, so I took an average of 4 runs.

Another reason I'd like this change is youtube accepts videos with higher
resolutions than 5120.
16384 is vp8's maximum resolution, so that should keep us amused for a
little longer.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/swscale_internal.h

@@ -34,7 +34,7 @@
 #define MAX_FILTER_SIZE 256
 
 #if ARCH_X86
-#define VOFW 5120
+#define VOFW 21502
 #else
 #define VOFW 2048 // faster on PPC and not tested on others
 #endif