KVM: x86: expose MSR_TSC_AUX to userspace

KVM: x86: expose MSR_TSC_AUX to userspace

commit 9dbe6cf941a6fe82933aef565e4095fb10f65023 upstream.

If we do not do this, it is not properly saved and restored across
migration.  Windows notices due to its self-protection mechanisms,
and is very upset about it (blue screen of death).

Cc: Radim Krcmar <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[bwh: Backported to 3.2:
 - We didn't yet have the switch() in kvm_init_msr_list as MPX is not
   supported at all
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>