platform/x86: ideapad-laptop: add "always on USB charging" control support

Certain models have a so-called "always on USB charging" feature,
which enables USB charging even when the computer is turned off
or suspended, and which may be controlled/queried using the
SALS/HALS ACPI methods. Expose this functionality via a new device
attribute (usb_charging). Tested on: Lenovo YOGA 520-14IKB 80X8

Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Link: https://lore.kernel.org/r/20210203215403.290792-28-pobrn@protonmail.com


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>