On some devices the USB Type-C port power (USB PD 2.0) negotiation is
done by a separate port-controller IC, while the current limit is
controlled through another (charger) IC.

It has been decided to model this by modelling the external Type-C
power brick (adapter/charger) as a power-supply class device which
supplies the charger-IC, with its voltage-now and current-max representing
the negotiated voltage and max current draw.

This commit adds support for this to the bq24190_charger driver by adding
an external_power_changed callback and calling
power_supply_set_input_current_limit_from_supplier from this callback.
This callback will only get called if the bq24190 has a parent-supply.

Note this replaces the functionality to get the current-limit from an
extcon device, which will be removed in a follow-up commit.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Tony Lindgren <tony@atomide.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>