ARM: dts: vf500-colibri: add Colibri VF50 support

Add Colibri VF50 device tree files vf500-colibri.dtsi and
vf500-colibri-eval-v3.dts, in line with the Colibri VF61 device tree
files. However, to minimize dupplication we also add vf-colibri.dtsi
and vf-colibri-eval-v3.dtsi which contain the common device tree
nodes.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>