xen/arm: setup: Call unregister_init_virtual_region() after the last init function

discard_init_modules() is an init function, if the path contains a
BUG() or WARN() we still want to get the full stack trace.

The init virtual region is now kept after the last init function has
been called.

Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>

xen/arch/arm/setup.c

@@ -72,10 +72,11 @@ domid_t __read_mostly max_init_domid;
 
 static __used void init_done(void)
 {
+    discard_initial_modules();
+
     /* Must be done past setting system_state. */
     unregister_init_virtual_region();
 
-    discard_initial_modules();
     free_init_memory();
     startup_cpu_idle_loop();
 }