KVM: Convert mask notifiers to use irqchip/pin instead of gsi

Devices register mask notifier using gsi, but irqchip knows about
irqchip/pin, so conversion from irqchip/pin to gsi should be done before
looking for mask notifier to call.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>