KVM: TDX: Make pmu_intel.c ignore guest TD case

TDX KVM doesn't support PMU yet, it's future work of TDX KVM support as
another patch series. For now, handle TDX by updating vcpu_to_lbr_desc()
and vcpu_to_lbr_records() to return NULL.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Co-developed-by: Tony Lindgren <tony.lindgren@linux.intel.com>
Signed-off-by: Tony Lindgren <tony.lindgren@linux.intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 - Add pragma poison for to_vmx() (Paolo)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>