Add simplebus_detach()

[oskar.holmlund_ohdata.se]

Summary

To add simplebus to syscon_generic.c ( D26402 ) a detach function are needed.

A problem with this code is if another driver creates the memory for the simplebus_devinfo structure and calls simplebus_add_device() the detach function will free the memory.
any suggestions?

[mmel]

Already committed as part of other change.