platform/x86: asus-wmi: Add support for multiple kbd led handlers

platform/x86: asus-wmi: Add support for multiple kbd led handlers

Some devices, such as the Z13 have multiple Aura devices connected
to them by USB. In addition, they might have a WMI interface for
RGB. In Windows, Armoury Crate exposes a unified brightness slider
for all of them, with 3 brightness levels.

Therefore, to be synergistic in Linux, and support existing tooling
such as UPower, allow adding listeners to the RGB device of the WMI
interface. If WMI does not exist, lazy initialize the interface.

Since hid-asus and asus-wmi can both interact with the led objects
including from an atomic context, protect the brightness access with a
spinlock and update the values from a workqueue. Use this workqueue to
also process WMI keyboard events, so they are handled asynchronously.

Acked-by: Benjamin Tissoires <bentiss@kernel.org>
Signed-off-by: Antheas Kapenekakis <lkml@antheas.dev>
Reviewed-by: Denis Benato <benato.denis96@gmail.com>
Link: https://patch.msgid.link/20260122075044.5070-8-lkml@antheas.dev
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>