platform/x86: ideapad-laptop: Fix FnLock not remembered among boots

On devices supported by ideapad-laptop, the HW/FW can remember the
FnLock state among boots. However, since the introduction of the FnLock
LED class device, it is turned off while shutting down, as a side effect
of the LED class device unregistering sequence.

Many users always turn on FnLock because they use function keys much
more frequently than multimedia keys. The behavior change is
inconvenient for them. Thus, set LED_RETAIN_AT_SHUTDOWN on the LED class
device so that the FnLock state gets remembered, which also aligns with
the behavior of manufacturer utilities on Windows.

Fixes: 07f48f66 ("platform/x86: ideapad-laptop: add FnLock LED class device")
Cc: stable@vger.kernel.org
Signed-off-by: Rong Zhang <i@rong.moe>
Reviewed-by: Hans de Goede <hansg@kernel.org>
Link: https://lore.kernel.org/r/20250707163808.155876-2-i@rong.moe


Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>