Dualcpu: Move NS mailbox thread management to RTOS specific file

The NS mailbox thread management is NS RTOS specific.

- Add a new tfm_ns_mailbox_rtos_api.c to collect all the NS mailbox
  APIs which rely on RTOS specific implementations.
- Move those API implementations from platform to
  tfm_ns_mailbox_rtos_api.c.
- Rename those APIs to replace HAL keyword with OS keyword, to
  indicate that their implementations are RTOS specific.

Change-Id: Ic2885bc1676964719d1524b39d6518444610e1aa
Signed-off-by: David Hu <david.hu@arm.com>
diff --git a/cmake/install.cmake b/cmake/install.cmake
index dd1ffc8..cb7f100 100644
--- a/cmake/install.cmake
+++ b/cmake/install.cmake
@@ -113,8 +113,9 @@
 
 if (TFM_MULTI_CORE_TOPOLOGY)
     install(FILES       ${INTERFACE_SRC_DIR}/tfm_ns_mailbox.c
-                        ${INTERFACE_SRC_DIR}/tfm_multi_core_api.c
+                        ${INTERFACE_SRC_DIR}/tfm_multi_core_ns_api.c
                         ${INTERFACE_SRC_DIR}/tfm_multi_core_psa_ns_api.c
+                        ${INTERFACE_SRC_DIR}/tfm_ns_mailbox_rtos_api.c
             DESTINATION ${INSTALL_INTERFACE_SRC_DIR})
 else()
     install(FILES       ${INTERFACE_SRC_DIR}/tfm_ns_interface.c