An asserted pirq can be disabled and the corresponding GSIs
should then go down to 0. However, because of the conditional in
ich9_lpc_update_by_pirq, the legacy 8259 pin could remain stuck to 1.
Reviewed-by: Efimov Vasily <real@ispras.ru> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>