KVM: x86: Hyper-V tsc page setup

Lately tsc page was implemented but filled with empty
values. This patch setup tsc page scale and offset based
on vcpu tsc, tsc_khz and  HV_X64_MSR_TIME_REF_COUNT value.

The valid tsc page drops HV_X64_MSR_TIME_REF_COUNT msr
reads count to zero which potentially improves performance.

Signed-off-by: Andrey Smetanin <asmetanin@virtuozzo.com>
Reviewed-by: Peter Hornyack <peterhornyack@google.com>
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Roman Kagan <rkagan@virtuozzo.com>
CC: Denis V. Lunev <den@openvz.org>
[Computation of TSC page parameters rewritten to use the Linux timekeeper
 parameters. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>