NEON optimised yuv to rgb conversion

- along the lines of the SSE chroma upsampling.
Total speedup is ~30%.

4% speed loss on YuvToRgbXX conversion using tables instead
of 14-bit fixed precision. TODO(later): investigate, and compare
to x86.

see http://code.google.com/p/webp/issues/detail?id=134

Change-Id: Idc2261037cd13b4553ca20ecc4c4007099c37009

src/dsp/upsampling.c

@@ -327,6 +327,11 @@ void WebPInitUpsamplers(void) {
     if (VP8GetCPUInfo(kSSE2)) {
       WebPInitUpsamplersSSE2();
     }
+#endif
+#if defined(WEBP_USE_NEON)
+    if (VP8GetCPUInfo(kNEON)) {
+      WebPInitUpsamplersNEON();
+    }
 #endif
   }
 #endif  // FANCY_UPSAMPLING
@@ -347,6 +352,11 @@ void WebPInitPremultiply(void) {
     if (VP8GetCPUInfo(kSSE2)) {
       WebPInitPremultiplySSE2();
     }
+#endif
+#if defined(WEBP_USE_NEON)
+    if (VP8GetCPUInfo(kNEON)) {
+      WebPInitPremultiplyNEON();
+    }
 #endif
   }
 #endif  // FANCY_UPSAMPLING