test,arch: fix few odd suffix include paths

Fix some more legacy include paths found in files with unusual suffixes.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>

tests/unit/math_extras/tests.inc

@@ -5,7 +5,7 @@
  */
 
 #include <ztest.h>
-#include <sys/math_extras.h>
+#include <zephyr/sys/math_extras.h>
 #include <inttypes.h>
 
 static void VNAME(u32_add)(void)

tests/unit/util/maincxx.cxx

@@ -4,8 +4,8 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-#include <ztest.h>
-#include <sys/util.h>
+#include <zephyr/ztest.h>
+#include <zephyr/sys/util.h>
 #include <string.h>
 
 #include "test.inc"

tests/unit/util/test.inc

@@ -4,8 +4,8 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-#include <ztest.h>
-#include <sys/util.h>
+#include <zephyr/ztest.h>
+#include <zephyr/sys/util.h>
 #include <string.h>
 
 /**