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/board/fvp/fvp_pm.c b/plat/arm/board/fvp/fvp_pm.c
index ecf0b01..42dec8d 100644
--- a/plat/arm/board/fvp/fvp_pm.c
+++ b/plat/arm/board/fvp/fvp_pm.c
@@ -20,6 +20,7 @@
 #include <platform_def.h>
 
 #include "fvp_private.h"
+#include "../drivers/arm/gic/v3/gicv3_private.h"
 
 
 #if ARM_RECOM_STATE_ID_ENC