stand/kshim: Implement bus_detach_children

[jhb]

Summary

While here, update bus_generic_detach to delete devices as in the
kernel.

[markj]

stand/kshim/bsd_kernel.c

689

device_delete_children() will call device_detach() on each child again, but I think that's harmless.

[jhb]

stand/kshim/bsd_kernel.c

689

Yes, and this is also true in the kernel implementation. The difference is that here we don't delete any devices if a child device vetos the detach operation.