arm64: dts: add CPU topology on Juno

This patch adds CPU topology on Juno. It will be useful for ther other
IP blocks depending on this topology.

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Liviu Dudau <Liviu.Dudau@arm.com>
Cc: Jon Medhurst (Tixy) <tixy@linaro.org>