replace pci_enable_msi_{exact_range} with pci_alloc_irq_vectors

[Christoph Hellwig]

Hi all,

this series switch the remaining users of pci_enable_msi_{exact_range}
(accounting for ahci and nvme being done through other channels) to
use the pci_alloc_irq_vectors helper instead and thus simplify the
interrupt code in those drivers a lot.  I decided to post it as a
series to everyone involved and linux-pci so that we can get a bit of
cross-review given that I have none of the involved hardware myself.