ARM: dts: omap3-tobi: Add SMSC911X node

The Tobi expansion boards embeds a SMSC LAN8700 PHY. Add the
corresponding node into the DT. The regulators are not designed
to be turned off.

Signed-off-by: Florian Vaussard <florian.vaussard@epfl.ch>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>