smbus: allow child devices to be added via hints

[avg]

Summary

This will allow to add slave drivers in the same fashion as for iicbus.

Also, allow other code to add a child device and set its 'addr' ivar.
The ivar can only be set if it's unset, it can not be changed.
That could be used, for example, by a platform driver that has
a precise description of the hardware and, thus, knows what drivers
can handle what slaves.

The slave auto-probing code is unsafe and broken because it uses
7-bit slave addresses. It's going to be removed.

Note: internally the driver uses address of zero as an unset address
while smbus_get_addr() returns it as -1 for compatibility reasons.
The address is expected to be unset only for children that do not
work with slaves like, for example, smb(4).

Test Plan

Tested with jedec_ts driver (coming).

[jhb]

sys/dev/smbus/smbus.c

117

Technically bus_pass_order aren't for the device orders but for the pass set in EARLY_DRIVER_MODULE(). You could define your own constants though (which is what ACPI does) for DEVICE_ORDER_HINTED and DEVICE_ORDER_PROBED or some such.

221

s/no/not/