ACPI: battery: create alarm sysfs attribute atomically

[ Upstream commit a231eed10ed5a290129fda36ad7bcc263c53ff7d ]

Let the power supply core register the attribute.
This ensures that the attribute is created before the device is
announced to userspace, avoid a race condition.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>