KVM: TDX: create/free TDX vcpu structure

Implement vcpu related stubs for TDX for create, reset and free.

For now, create only the features that do not require the TDX SEAMCALL.
The TDX specific vcpu initialization will be handled by KVM_TDX_INIT_VCPU.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 - Use lapic_in_kernel() (Nikolay Borisov)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>