uio: Convert uio_generic_pci to new intx masking API

The new PCI API provides both generic probing for 2.3 masking support
and check&mask in the interrupt handler.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>