Move GenerationCache to the utils directory.

Change-Id: I210ffa8f1d76a102bb7d971c649c20a74d03fbe6
diff --git a/libs/hwui/TextDropShadowCache.h b/libs/hwui/TextDropShadowCache.h
index b65d62a..16e2814 100644
--- a/libs/hwui/TextDropShadowCache.h
+++ b/libs/hwui/TextDropShadowCache.h
@@ -21,7 +21,7 @@
 
 #include <SkPaint.h>
 
-#include "GenerationCache.h"
+#include "utils/GenerationCache.h"
 #include "FontRenderer.h"
 #include "Texture.h"