[RFC 0/3]: hvc_console rework for platform without hard irqs

[Christian Borntraeger]

This patch set if my first attempt to make virtio_console usable on s390.
To do so, I had to change hvc_console, because s390 has no request_irq and
no free_irq.
I want to get feedback from the main users of hvc_console before I proceed.

The basic idea of this patch set is to remove the calls to request_irq and
free_irq and replace them with backend specific callbacks.

Please see the descriptions of the patches for further details:

1/3: hvc_console: rework setup to replace irq functions with callbacks
2/3: virtio_console: use virtqueue notification for hvc_console
3/3: s390: use virtio_console for KVM on s390