HID: asus: add support for the asus-wmi brightness handler

HID: asus: add support for the asus-wmi brightness handler

If the asus-wmi brightness handler is available, send the
keyboard brightness events to it instead of passing them
to userspace. If it is not, fall back to sending them to it.

Reviewed-by: Luke D. Jones <luke@ljones.dev>
Tested-by: Luke D. Jones <luke@ljones.dev>
Reviewed-by: Denis Benato <benato.denis96@gmail.com>
Acked-by: Benjamin Tissoires <bentiss@kernel.org>
Signed-off-by: Antheas Kapenekakis <lkml@antheas.dev>
Link: https://patch.msgid.link/20260122075044.5070-12-lkml@antheas.dev
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>