armv8r64-extras/classes: Add Zephyr domain config

Add configuration for a Zephyr domain to xen_dom0less_config.bbclass

Add the Zephyr passthrough device tree to xen-dom0less-devicetree.

Issue-Id: SCM-4386
Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
Change-Id: I79b9a3ec1b37b46caac85326ff6cb7bace6d1cec