kernel: change metadata for priv_stacks to const

The metadata array for priv_stacks doesn't change and
can be marked const so this can put in ROM.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>
diff --git a/scripts/gen_kobject_list.py b/scripts/gen_kobject_list.py
index 03882e7..2d54fcc 100755
--- a/scripts/gen_kobject_list.py
+++ b/scripts/gen_kobject_list.py
@@ -780,7 +780,7 @@
                      " priv_stacks[%d][Z_KERNEL_STACK_LEN(CONFIG_PRIVILEGED_STACK_SIZE)];\n"
                      % stack_counter)
 
-            fp.write("static struct z_stack_data stack_data[%d] = {\n"
+            fp.write("static const struct z_stack_data stack_data[%d] = {\n"
                      % stack_counter)
             counter = 0
             for _, ko in objs.items():