ideapad-laptop: Fn+M (Touchpad Toggle) not working on Lenovo ThinkBook 16 G4+ IAP

[Gillian Laurenti]

Hi,
The Fn+M touchpad toggle hotkey on the Lenovo ThinkBook 16 G4+ IAP
doesn't generate a keycode under Linux.
Pressing the key only triggers a generic WMI event in acpi_listen: wmi
PNP0C14:03 000000d0 00000000
Since the ideapad_laptop driver already handles these 0xD0 events by
reading the VPC status register, I did some testing on this model. It
looks like the touchpad toggle state is mapped to bit 6 of the
register.
Can we add parsing for bit 6 on 0xD0 events so the driver can report
the touchpad toggle keycode properly?

System Information:
Model: Lenovo ThinkBook 16 G4+ IAP
OS: Arch Linux
Kernel version: 6.18.31-1-lts