integral-image-dom0-live: Increase dom0 memory to 512M.

Ran outta memory shutting down a few times.
integral-image-dom0-live: Add 'iommu' parameter to Xen command line.

These seem to be a safe set of parameters to use for the IOMMU. We
force Xen to use the IOMMU. If no IOMMU is available Xen will refuse
to boot. Enable passthrough to PV guests (the NDVM) and make logging
verbose so we can verify things are as we expect. A good exercise here
is to reboot the NDVM and watch output from 'xl dmesg'. It should show
the IOMMU mapping and unmapping the device from dom0 (d0) and the NDVM
which is initially domain 1 (d1) and will have an increasing domain
number for each reboot.