Remove several warnings reported with W=1

Improved support for W=1 compilation flag by solving missing-prototypes
and old-style-definition warnings.

The libraries are compiling with warnings (which turn into errors with
the Werror flag).

Outside of libraries, some warnings cannot be fixed without heavy
structural changes.

Change-Id: I1668cf99123ac4195c2a6a1d48945f7a64c67f16
Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>

services/std_svc/spm/spm_main.c

 /*
- * Copyright (c) 2017-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -20,6 +20,7 @@
 #include <lib/utils.h>
 #include <lib/xlat_tables/xlat_tables_v2.h>
 #include <plat/common/platform.h>
+#include <services/spm_svc.h>
 #include <services/sprt_svc.h>
 #include <smccc_helpers.h>