q35: Suppress SMM BIOS initialization under KVM

Same as for i44fx: KVM does not support SMM yet. Signal it initialized
to Seabios to avoid failures.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
