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/bl2/bl2_main.c b/bl2/bl2_main.c
index 1deebc8..cb0519a 100644
--- a/bl2/bl2_main.c
+++ b/bl2/bl2_main.c
@@ -37,7 +37,7 @@
 #include <semihosting.h>
 #include <bl_common.h>
 #include <bl2.h>
-#include "debug.h"
+#include <debug.h>
 
 /*******************************************************************************
  * The only thing to do in BL2 is to load further images and pass control to