KVM: x86: Setup Hyper-V TSC page before Xen PV clocks (during clock update)

When updating paravirtual clocks, setup the Hyper-V TSC page before
Xen PV clocks.  This will allow dropping xen_pvclock_tsc_unstable in favor
of simply clearing PVCLOCK_TSC_STABLE_BIT in the reference flags.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Link: https://lore.kernel.org/r/20250201013827.680235-11-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>