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/av1/encoder/pickrst.c b/av1/encoder/pickrst.c
index 115f66f..308985e 100644
--- a/av1/encoder/pickrst.c
+++ b/av1/encoder/pickrst.c
@@ -14,7 +14,7 @@
 #include <limits.h>
 #include <math.h>
 
-#include "./aom_scale_rtcd.h"
+#include "config/aom_scale_rtcd.h"
 
 #include "aom_dsp/aom_dsp_common.h"
 #include "aom_dsp/binary_codes_writer.h"