ARM: bcm281xx: Board specific reboot code

This patch adds the code needed to trigger a reboot on the bcm281xx
family.

Signed-off-by: Markus Mayer <markus.mayer@linaro.org>
Reviewed-by: Tim Kryger <tim.kryger@linaro.org>
Reviewed-by: Matt Porter <matt.porter@linaro.org>
Reviewed-by: Alex Elder <alex.elder@linaro.org>
Acked-by: Christian Daudt <csd@broadcom.com>