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/include/drivers/io_driver.h b/include/drivers/io_driver.h
index 82dbbf1..5e3d132 100644
--- a/include/drivers/io_driver.h
+++ b/include/drivers/io_driver.h
@@ -31,7 +31,7 @@
 #ifndef __IO_DRIVER_H__
 #define __IO_DRIVER_H__
 
-#include "platform.h"   /* For MAX_IO_DEVICES */
+#include <platform.h>   /* For MAX_IO_DEVICES */
 
 
 /* Generic IO entity structure,representing an accessible IO construct on the