Core: Separate library code from spm_api.c file

- Moves library-model-only APIs into another file spm_api_func.c.
- Separates spm code into 3 parts: for library model (func), IPC model
  (ipc) and common.

Change-Id: I35bc43c21415e89c1f353a4c798aa3d8f69ec168
Signed-off-by: Mingyang Sun <mingyang.sun@arm.com>
diff --git a/secure_fw/spm/spm_api_ipc.c b/secure_fw/spm/spm_api_ipc.c
index 595a1a2..6443b52 100644
--- a/secure_fw/spm/spm_api_ipc.c
+++ b/secure_fw/spm/spm_api_ipc.c
@@ -4,6 +4,9 @@
  * SPDX-License-Identifier: BSD-3-Clause
  *
  */
+
+/* All the APIs defined in this file are used for IPC model. */
+
 #include <inttypes.h>
 #include <limits.h>
 #include <stdbool.h>