xen/passthrough: arm: release the DT devices assigned to a guest earlier

xen/passthrough: arm: release the DT devices assigned to a guest earlier

The toolstack may not have deassigned every device used by a guest.
Therefore we have to go through the device list and remove them before
asking the IOMMU drivers to release memory for this domain.

This can be done by moving the call to the release function when we
relinquish the resources. The IOMMU part will be destroyed later when
the domain is freed.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Signed-off-by: Robert VanVossen <robert.vanvossen@dornerworks.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>