ACPI / battery: Add handling for devices which wrongly report discharging state

On quite a few devices the battery code in the ACPI tables is buggy and
first checks the charging status bits of the charger-IC, and if those
report not charging it will report discharging, without looking at the
presence of AC power or at the battery dis(charge) current from the
fuel-gauge.

This causes the wrong status to be reported for the battery in the
following quite common scenario:

1) Plug in charger while battery is say half full, battery starts
charging, charging state bits indicate: pre-charge or fast-charge,
ACPI reported battery status is ok

2) When fully charged charging state bits indicate: end-of-charge,
ACPI reported battery status is ok

3) unplug the charger, wait 1 minute, replug. Now the battery voltage is
still above the start-charging threshold, so the charger will not start
charging to avoid wrecking the battery by repeatedly recharging the last 1%
capacity. The charger IC charging state bits now are all 0 (not-charging)
and the broken ACPI code wrongly translate this to "discharging" and ends
up setting the ACPI_BATTERY_STATE_DISCHARGING bit in its state field.

Reporting this "not charging" state as discharging is confusing for users,
making the user think his adapter/power-brick is broken or not properly
plugged in.

This commit adds a helper for handling the ACPI_BATTERY_STATE_DISCHARGING
state. This helper checks if we're an AC and the current going out of the
battery is 0 and in that case reports a status of "not charging" to
userspace rather then "discharging".

This replaces commit c68f0676 ("ACPI / battery: Add quirk for Asus
GL502VSK and UX305LA"), a previous fix for this which was reverted.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Daniel Drake <drake@endlessm.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>