automatic IRQ affinity for virtio

Hi Michael,

this series contains a couple cleanups for the virtio_pci interrupt
handling code, including a switch to the new pci_irq_alloc_vectors
helper, and support for automatic affinity by the PCI layer if the
consumers ask for it.  It then converts over virtio_blk to use this
functionality so that it's blk-mq queues are aligned to the MSI-X
vector routing.  I have a similar patch in the queue for virtio-scsi,
but that would require pulling in the SCSI tree, so I'm not sure if
you'd like it for this window, but if you do I can send it in another
series.  The third driver using per-CPU virtqueues is virtio_net,
but that will take some more time as I haven't started work on the
networking infrastructure yet.

Note that these patches require core IRQ changes from a stable
branch in the tip tree to be pulled in first:

	git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git irq/for-block

Gitweb:

	https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/log/?h=irq/for-block