arm: spear6xx: add labels to various nodes in spear600.dtsi

Having labels allows to more easily reference nodes in .dts files
including spear600.dtsi.

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>