Dualcpu: Execute dual-cpu init after RTX kernel init completes

NS mailbox initialization creates semaphore. CMSIS-RTOS v2 API
requires that semaphore creation API shall be called after
osKernelInitialize().
Move dual-cpu init, including NS mailbox init, after
osKernelInitialize() in main() in RTX implementation.

Signed-off-by: David Hu <david.hu@arm.com>
Change-Id: I1fc810c4bd9256555da882e9ba3a88a45d416aec
diff --git a/app/main_ns.c b/app/main_ns.c
index 850b6a6..70e54ed 100644
--- a/app/main_ns.c
+++ b/app/main_ns.c
@@ -167,12 +167,12 @@
         while(1);
     }
 
+    (void) osKernelInitialize();
+
 #ifdef TFM_MULTI_CORE_TOPOLOGY
     tfm_ns_multi_core_boot();
 #endif
 
-    (void) osKernelInitialize();
-
     /* Initialize the TFM NS interface */
     tfm_ns_interface_init();