x86/svm: enable TSC scaling

x86/svm: enable TSC scaling

TSC ratio enabling logic is inverted: we want to use it when we
are running in native tsc mode, i.e. when d->arch.vtsc is zero.

Also, since now svm_set_tsc_offset()'s calculations depend
on vtsc's value, we need to call hvm_funcs.set_tsc_offset() after
vtsc changes in tsc_set_info().

In addition, with TSC ratio enabled, svm_set_tsc_offset() will
need to do rdtsc. With that we may end up having TSCs on guest's
processors out of sync. d->arch.hvm_domain.sync_tsc which is set
by the boot processor can now be used by APs as reference TSC
value instead of host's current TSC.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>