All drivers use the default, so provide an inline version of it.  If we
ever need other queue mapping we can add an optional method back,
although supporting will also require major changes to the queue setup
code.

This provides better code generation, and better debugability as well.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NKeith Busch <keith.busch@intel.com>
Signed-off-by: NJens Axboe <axboe@fb.com>