board: boundary: Remove <common.h> and add needed includes

Remove <common.h> from this board vendor directory and when needed
add missing include files directly.

Signed-off-by: Tom Rini <trini@konsulko.com>

board/boundary/nitrogen6x/nitrogen6x.c

@@ -4,7 +4,6 @@
  * Copyright (C) 2013, Boundary Devices <info@boundarydevices.com>
  */
 
-#include <common.h>
 #include <command.h>
 #include <env.h>
 #include <init.h>