XEN Hypervisor cannot use more then 64 CPUs

Issue

• A system with more than 64 "Cores" (CPUs) only uses Core 0-63 for the DomUs.
• Pinning the DomU via xm vcpu-pin to a CPU higher than 63 results in a pinning to <CPU-Number given> % 64.
• xenmon.py also shows all CPUs higher than 63 as idle.
• The system is booted with numa=on or numa=1 in grub.conf