crypto: cavium - switch to pci_alloc_irq_vectors

pci_enable_msix has been long deprecated, but this driver adds a new
instance.  Convert it to pci_alloc_irq_vectors and greatly simplify
the code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>