powerpc mpc85xx: Use bus_generic_rman_*

• Consistently map SYS_RES_IOPORT to SYS_RES_MEMORY for bus_activate/deactivate/adjust/release_resource.

• Implement bus_map/unmap_resource.

• Add an implementation of bus_adjust_resource.

Reviewed by: jhibbits
Differential Revision: https://reviews.freebsd.org/D43434