xcl: PVH is only supported for >= Xen 4.4.0
xcl: PVH is only supported for >= Xen 4.4.0

PVH support broke cosmos for Xen 4.3.0 and below. Make the
necessary code build only on Xen 4.4.0 and above.

seemoo-lab/cosmos,cnplab/cosmos,seemoo-lab/cosmos,seemoo-lab/cosmos,cnplab/cosmos,seemoo-lab/cosmos,cnplab/cosmos,cnplab/cosmos