hwpmc: Avoid touching MSR_DEBUGCTLMSR inside VMs.
At least KVM in Proxmox seems not happy about it. Just to be safe
block it for all VMs, since it should just improve profile accuracy.
MFC after: 1 week
(cherry picked from commit 4e679d8aeaa86ce061b15c51fe9a5eae1eff7470)