machine: allow early use of machine_require_guest_memfd

Ask the ConfidentialGuestSupport object whether to use guest_memfd
for KVM-backend private memory.  This bool can be set in instance_init
(or user_complete) so that it is available when the machine is created.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
3 files changed