Dualcpu: Protect NS mailbox critical section in NS IRQ handler

Add tfm_ns_mailbox_hal_enter_critical_isr() and
tfm_ns_mailbox_hal_exit_critical_isr() to protect NS mailbox
critical access in NSPE IRQ handler.

Change-Id: I2fd0bcaa6044183fe00d524fb4b423c61ca43efd
Signed-off-by: David Hu <david.hu@arm.com>
diff --git a/interface/include/tfm_ns_mailbox.h b/interface/include/tfm_ns_mailbox.h
index a846e76..3340735 100644
--- a/interface/include/tfm_ns_mailbox.h
+++ b/interface/include/tfm_ns_mailbox.h
@@ -123,6 +123,20 @@
  */
 void tfm_ns_mailbox_hal_exit_critical(void);
 
+/**
+ * \brief Enter critical section of NSPE mailbox in IRQ handler.
+ *
+ * \note The implementation depends on platform specific hardware and use case.
+ */
+void tfm_ns_mailbox_hal_enter_critical_isr(void);
+
+/**
+ * \brief Enter critical section of NSPE mailbox in IRQ handler
+ *
+ * \note The implementation depends on platform specific hardware and use case.
+ */
+void tfm_ns_mailbox_hal_exit_critical_isr(void);
+
 #ifdef __cplusplus
 }
 #endif