power: supply: core: add POWER_SUPPLY_HEALTH_NO_BATTERY

Some chargers can keep the system powered from the mains even when no
battery is present. It this case none of the currently defined health
statuses applies. Add a new status to report that no battery is present.

Suggested-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>