Interface: Make the NS interface functions common

This patch implements common TF-M NS interface functions defined in
tfm_ns_interface.h, by calling the os_wrapper APIs.
With this change, the NSPE does not need to implement the TF-M NS
interface functions but only the os_wrapper APIs.
Still NSPE can overwrite the whole TF-M NS interface functions to
fulfill their special requirements.

Change-Id: Ifec47b99d6cba73acd94cfc0fde584f08333ab3c
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
diff --git a/interface/include/tfm_ns_interface.h b/interface/include/tfm_ns_interface.h
index 89b29471..21857be 100644
--- a/interface/include/tfm_ns_interface.h
+++ b/interface/include/tfm_ns_interface.h
@@ -32,9 +32,9 @@
  *
  * \return Returns the same return value of the requested veneer function
  */
-uint32_t tfm_ns_interface_dispatch(veneer_fn fn,
-                                   uint32_t arg0, uint32_t arg1,
-                                   uint32_t arg2, uint32_t arg3);
+int32_t tfm_ns_interface_dispatch(veneer_fn fn,
+                                  uint32_t arg0, uint32_t arg1,
+                                  uint32_t arg2, uint32_t arg3);
 
 /**
  * \brief NS interface, Initialise the NS interface
@@ -46,7 +46,7 @@
  *
  * \return  A value according to \ref enum tfm_status_e
  */
-enum tfm_status_e tfm_ns_interface_init();
+enum tfm_status_e tfm_ns_interface_init(void);
 #ifdef __cplusplus
 }
 #endif