powerpc psim: Use bus_generic_rman_*

[jhb]

Summary

• Split out bits of iobus_activate/deactive_resource to implement iobus_map/unmap_resource.

• Use bus_generic_rman_* methods in several bus methods to handle memory and I/O port resources.

• Add an implementation of bus_adjust_resource.

[jhibbits]

Does psim even still work?

[grehan]

In D43433#991937, @jhibbits wrote:

Does psim even still work?

Let me give it a try. Seems to still be maintained in upstream gdb.

[imp]

I with there was a 'no objection' button here.
But I think between the helper and the small code reorg this is what we want.
I'm not completely sure, and the lack of testability makes me uneasy.
But I think they are OK enough for me to tick the 'yes' button failing to find any reason to say no.