blk-mq: allow passing in an external queue mapping V3

[Christoph Hellwig]

This series is the remainder of the earlier "automatic interrupt affinity for
MSI/MSI-X capable devices" series, and make uses of the new irq-level
interrupt / queue mapping code in blk-mq, as well as allowing the driver
to pass in such a mask obtained from the (PCI) interrupt code.  To fully
support this feature in drivers the final third in the PCI layer will
be needed as well.

A git tree is available at:

   git://git.infradead.org/users/hch/block.git block-queue-mapping.2

Gitweb:

   http://git.infradead.org/users/hch/block.git/shortlog/refs/heads/block-queue-mapping.2

Changes since V2:
 - major rework of the core IRQ affinity code to support sibling maps
 - reworked the block code to use the above
 
Changes since V1:
 - rebased on top of Linux 4.8-rc4

Changes since automatic interrupt affinity for MSI/MSI-X capable devices V3:
 - a trivial cleanup in blk_mq_create_mq_map pointed out by Alexander