ofw_pcib: Use bus_generic_rman_*

[jhb]

Summary

• 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.

[jhb]

Booted this series on RISC-V (QEMU), armv7 (RPI), and aarch64 (same RPI).