ACPI: SBS: manage alarm sysfs attribute through psy core

[ Upstream commit 6bad28cfc30988a845fb3f59a99f4b8a4ce8fe95 ]

Let the power supply core register the attribute.

This ensures that the attribute is created before the device is
announced to userspace, avoiding 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>