ARM: dts: i.MX51: Add W1 devicetree node

This patch adds the missing W1 (onewire) devicetree node for i.MX51 CPUs.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>