skd: use pci_alloc_irq_vectors

Switch the skd driver to use pci_alloc_irq_vectors.  We need to two calls to
pci_alloc_irq_vectors as skd only supports multiple MSI-X vectors, but not
multiple MSI vectors.

Otherwise this cleans up a lot of cruft and allows to a lot more common code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>