SSE2 version of simple in-loop filtering

~10% faster decoding

Patch by Somnath Banerjee (somnath at google dot com)

Change-Id: I200db408272b4f61cda9d9261d2d4370a698d6c4

src/dec/vp8i.h

@@ -337,6 +337,14 @@ extern VP8LumaFilterFunc VP8HFilter16i;
 extern VP8ChromaFilterFunc VP8VFilter8i;  // filtering u and v altogether
 extern VP8ChromaFilterFunc VP8HFilter8i;
 
+typedef enum {
+  kSSE2,
+  kSSE3
+} CPUFeature;
+// returns true if the CPU supports the feature.
+typedef int (*VP8CPUInfo)(CPUFeature feature);
+extern VP8CPUInfo VP8DecGetCPUInfo;
+
 //-----------------------------------------------------------------------------
 
 #if defined(__cplusplus) || defined(c_plusplus)