On devicetree using platforms the devicetree can provide info on which
power-supplies supply another power-supply through phandles.

This commit adds support for providing this info on non devicetree
platforms through the platform code setting a supplied-from
device-property on the power-supplies parent device.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>