platform/x86: x86-android-tablets: Add battery swnode support

power_supply_get_battery_info() which is used by charger and fuel-gauge
drivers on x86-android-tablets, expects the battery properties to be
described in a stand-alone battery fwnode which is then referenced
from both the charger and fuel-gauge device's fwnodes.

Add support for registering + unregistering a swnode for this.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220205191356.225505-1-hdegoede@redhat.com