scsi: vmw_pvscsi: switch to pci_alloc_irq_vectors

And simplify the interrupt handler by splitting the INTx case that needs
to deal with shared interrupts into a separate helper.

[mkp: typo fixage]

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jim Gill <jgill@vmware.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>