- Add support for using MSI instead of INTx, controllable via the tunable

- Add support for using MSI instead of INTx, controllable via the tunable
  hw.ral.msi_disable (defaulting to using MSI).
- Probe with BUS_PROBE_DEFAULT instead of 0.
- Nuke code setting PCI_POWERSTATE_D0; pci(4) already does that for type 0
  devices.
- Use PCIR_BAR instead of a homegrown macro.
- There's no need to keep track of resource IDs.
- Release resources again in case attaching fails.
- Quiesce the interrupt before detaching.
- Sprinkle const.
- Use DEVMETHOD_END.
- Use NULL instead of 0 for pointers.
- Trim headers.
- Nuke dupe $FreeBSD$.

MFC after:	1 week