i386/tdx: Don't synchronize guest tsc for TDs

i386/tdx: Don't synchronize guest tsc for TDs

TSC of TDs is not accessible and KVM doesn't allow access of
MSR_IA32_TSC for TDs. To avoid the assert() in kvm_get_tsc, make
kvm_synchronize_all_tsc() noop for TDs,

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Reviewed-by: Connor Kuehl <ckuehl@redhat.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250508150002.689633-40-xiaoyao.li@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>