ACPI: battery: include linux/power_supply.h

acpi/battery.h uses 'struct power_supply *', but fails to
include/create any declaration of the type. Include linux/
power_supply.h to fix that.

Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
[ rjw: Subject edit ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>