dm: core: add support for device re-parenting

In common clock framework the relation b/w parent and child clocks is
determined based on the udevice parent/child information. A clock
parent could be changed based on devices needs. In case this is happen
the functionalities for clock who's parent is changed are broken. Add
a function that reparent a device. This will be used in clk-uclass.c
to reparent a clock device.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reviewed-by: Simon Glass <sjg@chromium.org>