power: core: add power supply APIs

Rename power_supply_set_charging_by to power_supply_set_online to
more accurately reflect the intent of the API.

Add power_supply_set_charge_type to enable a charger driver to set
a POWER_SUPPLY_PROP_CHARGE_TYPE. Ultimately this is handled like
a request, the receiving charger driver then can handle the request
and report the adequate POWER_SUPPLY_PROP_CHARGE_TYPE once necessary
action has been taken.

Change-Id: Idf4760c7d6c0f61a9eccc656cd469a6ac5fdc6cd
Signed-off-by: David Keitel <dkeitel@codeaurora.org>