board: zyxel: 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>
---
Cc: Tony Dinh <mibodhi@gmail.com>
Cc: Luka Perkov <luka.perkov@sartura.hr>