PCI/portdrv: Support multiple interrupts for MSI as well as MSI-X
Root Ports can generate several different interrupts using either MSI or
MSI-X, but we only support that for MSI-X. Ports that support MSI but not
MSI-X are currently limited to sharing a single interrupt.
Rename pcie_port_enable_msix() to pcie_port_enable_irq_vec() and extend it
to support multiple interrupts using either MSI-X (preferred) or MSI.