arm: spear6xx: use node labels in spear600-evb.dts

Now that we have introduced node labels in spear600.dtsi, we can use
them for spear600-evb.dts.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>