Kernel: Add mechanism to make some memory read-only after init finishes

You can now use the READONLY_AFTER_INIT macro when declaring a variable
and we will put it in a special ".ro_after_init" section in the kernel.

Data in that section remains writable during the boot and init process,
and is then marked read-only just before launching the SystemServer.

This is based on an idea from the Linux kernel. :^)

Kernel/VM/MemoryManager.h

@@ -141,6 +141,8 @@ public:
 
     PageFaultResponse handle_page_fault(const PageFault&);
 
+    void protect_readonly_after_init_memory();
+
     static void enter_process_paging_scope(Process&);
     static void enter_space(Space&);