power: supply: sc27xx: Allow to change the battery full capacity

The battery full capacity can be affected by the temperature or the
servicing time or other factors, so some platforms will track the
real battery full capacity in charger manager service. Thus we should
allow to change the battery full capacity by setting the
'POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN' property as writeable.

Signed-off-by: Yuanjiang Yu <yuanjiang.yu@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang7@gmail.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>