arm/dom0less: assign dom0less guests to cpupools

arm/dom0less: assign dom0less guests to cpupools

Introduce domain-cpupool property of a xen,domain device tree node,
that specifies the cpupool device tree handle of a xen,cpupool node
that identifies a cpupool created at boot time where the guest will
be assigned on creation.

Add member to the xen_domctl_createdomain public interface so the
XEN_DOMCTL_INTERFACE_VERSION version is bumped.

Add public function to retrieve a pool id from the device tree
cpupool node.

Update documentation about the property.

Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com>