cmake: generate rtcd headers in config subdir.

Move rtcd header outputs to config subdir of config dir,
and update include sites.

Change-Id: I25c5f1808a091f3727934adc274637ebdcdcb1cf
diff --git a/test/hash_test.cc b/test/hash_test.cc
index 0f6905a..e9f7f63 100644
--- a/test/hash_test.cc
+++ b/test/hash_test.cc
@@ -13,7 +13,7 @@
 #include <new>
 
 #include "config/aom_config.h"
-#include "./av1_rtcd.h"
+#include "config/av1_rtcd.h"
 
 #include "aom_ports/aom_timer.h"
 #include "av1/encoder/hash.h"