machine: allowed/required kernel-irqchip support

The code using kernel-irqchip property requires 'allowed/required'
functionality. Replace machine's kernel_irqchip field with two fields
representing the new functionality and expose them through wrappers.

Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
