armv8r64-extras/xen-dom0less-stack: Introduce Xen dom0less stack recipe

Create a helper recipe which builds the linked image defined in
XEN_DOM0LESS_LINUX_IMAGE and its dependencies.

Set IMAGE_LINK_NAME to the same name in xen_dom0less_image.bbclass

Make this recipe the target of the virtualization Kas file.

Issue-Id: SCM-4386
Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
Change-Id: I0d40cb35db6788c5ff80a7cedfa9de17ff0de307