dm: core: Allow uclass to set up a device's child before it is probed

dm: core: Allow uclass to set up a device's child before it is probed

Some buses need to set up their devices before they can be used. This setup
may well be common to all buses in a particular uclass. Support a common
pre-probe method for the uclass, called before any bus devices are probed.

Signed-off-by: Simon Glass <[email protected]>
Reviewed-by: Masahiro Yamada <[email protected]>