Add support for Wandboard Quad

Add support for the Quad version of Wandboard; fix compile warning resulting
from having 2G of memory.

Signed-off-by: Tapani Utriainen <tapani@technexion.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Acked-by: Stefano Babic <sbabic@denx.de>