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>
diff --git a/plat/arm/css/sgi/sgi_bl31_setup.c b/plat/arm/css/sgi/sgi_bl31_setup.c
index 8fa5b01..ba050d5 100644
--- a/plat/arm/css/sgi/sgi_bl31_setup.c
+++ b/plat/arm/css/sgi/sgi_bl31_setup.c
@@ -13,6 +13,7 @@
 #include <drivers/arm/css/css_mhu_doorbell.h>
 #include <drivers/arm/css/scmi.h>
 #include <plat/arm/common/plat_arm.h>
+#include <plat/common/platform.h>
 
 #include <sgi_ras.h>
 #include <sgi_variant.h>
@@ -35,7 +36,7 @@
 		.ring_doorbell = &mhuv2_ring_doorbell,
 };
 
-scmi_channel_plat_info_t *plat_css_get_scmi_info()
+scmi_channel_plat_info_t *plat_css_get_scmi_info(void)
 {
 	if (sgi_plat_info.platform_id == RD_N1E1_EDGE_SID_VER_PART_NUM)
 		return &rd_n1e1_edge_scmi_plat_info;
@@ -43,7 +44,7 @@
 		return &sgi575_scmi_plat_info;
 	else
 		panic();
-};
+}
 
 void bl31_early_platform_setup2(u_register_t arg0, u_register_t arg1,
 				u_register_t arg2, u_register_t arg3)
diff --git a/plat/arm/css/sgi/sgi_interconnect.c b/plat/arm/css/sgi/sgi_interconnect.c
index e86c760..e9cd812 100644
--- a/plat/arm/css/sgi/sgi_interconnect.c
+++ b/plat/arm/css/sgi/sgi_interconnect.c
@@ -1,11 +1,12 @@
 /*
- * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2018-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
 #include <arch_helpers.h>
 #include <common/debug.h>
+#include <plat/arm/common/plat_arm.h>
 
 /*
  * For SGI575 which support FCM (with automatic interconnect enter/exit),
diff --git a/plat/arm/css/sgi/sgi_topology.c b/plat/arm/css/sgi/sgi_topology.c
index f9dbdef..7aa9e40 100644
--- a/plat/arm/css/sgi/sgi_topology.c
+++ b/plat/arm/css/sgi/sgi_topology.c
@@ -5,6 +5,7 @@
  */
 
 #include <plat/arm/common/plat_arm.h>
+#include <plat/common/platform.h>
 
 #include <sgi_variant.h>