ofw_pcib: Use bus_generic_rman_*

ofw_pcib: Use bus_generic_rman_*

- Implement bus_map/unmap_resource pulling bits from the previous
  ofw_pcib_activate/deactivate_resource.  One difference here is that
  the bus_unmap_resource implementation uses bus_space_unmap instead
  of pmap_unmapdev as a complement to the existing use of bus_space_map.

- Use bus_generic_rman_* in various routines for memory and I/O port
  resources.

- Use pci_domain_* for PCI_RES_BUS in
  ofw_pcib_activate/deactivate_resource.

Reviewed by:	imp
Differential Revision:	https://reviews.freebsd.org/D43441