power: supply: cw2015: Add CHARGE_NOW support

CHARGE_NOW is expected by some user software (such as waybar)
instead of 'CAPACITY', in order to correctly calculate remaining battery
life.

Signed-off-by: Martin Ashby <martin@ashbysoft.com>
Reviewed-by: Tobias Schramm <t.schramm@manjaro.org>
Tested-by: Tobias Schramm <t.schramm@manjaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>