vmw_pvrdma: switch to pci_alloc_irq_vectors

.. and greatly clean up the irq handling boilerplate code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Adit Ranadive <aditr@vmware.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>