Make use of user/system includes more consistent

Make codebase consistent in its use of #include "" syntax for
user includes and #include <> syntax for system includes.

Fixes ARM-software/tf-issues#65

Change-Id: If2f7c4885173b1fd05ac2cde5f1c8a07000c7a33
diff --git a/plat/fvp/aarch64/plat_common.c b/plat/fvp/aarch64/plat_common.c
index dd362f0..338141c 100644
--- a/plat/fvp/aarch64/plat_common.c
+++ b/plat/fvp/aarch64/plat_common.c
@@ -30,7 +30,7 @@
 
 #include <assert.h>
 #include <arch_helpers.h>
-#include "debug.h"
+#include <debug.h>
 #include <platform.h>
 #include <xlat_tables.h>