KVM: SVM: force new asid on vcpu migration

If a migrated vcpu matches the asid_generation value of the target pcpu,
there will be no TLB flush via TLB_CONTROL_FLUSH_ALL_ASID.

The check for vcpu.cpu in pre_svm_run is meaningless since svm_vcpu_load
already updated it on schedule in.

Such vcpu will VMRUN with stale TLB entries.

Based on original patch from Joerg Roedel (http://patchwork.kernel.org/patch/10021/)

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Acked-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>