power: supply: axp288_charger: Drop platform_data dependency

When the axp288_charger driver was originally merged, it was merged with
a dependency on some other driver providing platform data for it.

However the battery-data-framework which should provide that data never
got merged, so the axp288_charger as merged upstream has never worked,
its probe method simply always returns -ENODEV.

This commit removes the dependency on the platform_data instead reading
back the charging current and charging voltage that the firmware has set
and using those values as the maximum values the user may set.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>