ARM: bcm281xx: DT changes for reboot code

This patch adds the device tree bindings for the bcm281xx reboot code.

Signed-off-by: Markus Mayer <markus.mayer@linaro.org>
Reviewed-by: Tim Kryger <tim.kryger@linaro.org>
Acked-by: Christian Daudt <csd@broadcom.com>