KVM: support device deassignment

Support device deassignment, it can be used in device hotplug.

Signed-off-by: Weidong Han <weidong.han@intel.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

diff --cc include/linux/kvm_host.h
Simple merge

diff --cc virt/kvm/kvm_main.c
Simple merge

diff --cc virt/kvm/vtd.c
Simple merge