brcm63xx: work around boot failures with squashfs on BCM6368

Due to the LWL/LWR SMP issue on BCM6368, booting with squash might fail
if the rootfs is not word aligned. As a quick fix, work around it by
ensuring this condition is always true.

Reported-by: Álvaro Fernández Rojas <noltari@gmail.com>
Signed-off-by: Jonas Gorski <jogo@openwrt.org>

SVN-Revision: 47380