Update the handling of interrupts on the generic PCIe driver:

• Use the interrupt-map property to route interrupts
• Remove the IRQ rman, it's now unneeded
• Support MSI/MSI-X interrupts

With this I'm able to use the two NICs I've tested (em and msk), however
while I can boot with an AHCI devie attached it fails when any drives are
connected.

Obtained from: ABT Systems Ltd
Sponsored by: SoftIron Inc