power_supply: get_by_name and set_charged functionality

This adds a function that indicates that a battery is fully charged.
It also includes functions to get a power_supply device from the class
of registered devices by name reference. These can be used to find a
specific battery to call power_supply_set_battery_charged() on.

Some battery drivers might need this information to calibrate
themselves.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Ian Molton <spyro@f2s.com>
Cc: Anton Vorontsov <cbou@mail.ru>
Cc: Matt Reimer <mreimer@vpop.net>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>