ACPI / battery: Safe unregistering of hooks

ACPI / battery: Safe unregistering of hooks

A hooking API was implemented for 4.17 in 834530b64262889f followed
by hooks for Thinkpad laptops in dcd9abe2d03dc0fe. The Thinkpad
drivers did not support the Thinkpad 13 and the hooking API crashes
on unsupported batteries by altering a list of hooks during unsafe
iteration. Thus, Thinkpad 13 laptops could no longer boot.

Additionally, a lock was kept in place and debugging information was
printed out of order.

Fixes: 834530b64262 (battery: Add the battery hooking API)
Cc: 4.17+ <stable@vger.kernel.org> # 4.17+
Signed-off-by: Jouke Witteveen <j.witteveen@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>