Interface: Clean up the tfm_api.h header file

This file does not look like an "interface" file as it contains
some SPM internal usage definitions.

This patch:
- Moves the SPM internal definitions to spm.h.
- Use the error codes in `internal_status_code.h` instead of the
  ones in tfm_api.h.
- Removes error codes in tfm_api.h.
- Renames tfm_api.h to tfm_veneers.h to reflect what it does.
- Corresponding changes in source files.

Change-Id: Iba5d1aae6837c9f0bf52c9a0c456023d19a735ea
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
diff --git a/cmake/install.cmake b/cmake/install.cmake
index 064fc5b..43f8cb1 100644
--- a/cmake/install.cmake
+++ b/cmake/install.cmake
@@ -33,7 +33,7 @@
 install(FILES       ${CMAKE_BINARY_DIR}/generated/interface/include/psa_manifest/sid.h
         DESTINATION ${INSTALL_INTERFACE_INC_DIR}/psa_manifest)
 
-install(FILES       ${INTERFACE_INC_DIR}/tfm_api.h
+install(FILES       ${INTERFACE_INC_DIR}/tfm_veneers.h
                     ${INTERFACE_INC_DIR}/tfm_ns_interface.h
         DESTINATION ${INSTALL_INTERFACE_INC_DIR})