[REGRESSION] Backlight control broken on Dell G15 5515 since 6.1

[Youssef Aly <youssefaswad@gmail.com>]

Hello,

The backlight control has been broken on Dell G15 5515 since 6.1, it
is always at full brightness, this is only the case in hybrid (mux)
graphics mode.

As per the output of lsmod the nvidia_wmi_ec_backlight is loaded:
nvidia_wmi_ec_backlight    16384  0
video                  61440  5
nvidia_wmi_ec_backlight,dell_wmi,amdgpu,dell_laptop,nvidia_modeset
wmi                    36864  7
video,nvidia_wmi_ec_backlight,alienware_wmi,dell_wmi,wmi_bmof,dell_smbios,dell_wmi_descriptor

but it is not present in /sys/class/backlight, only amdgpu_bl1 is
present which is not functional
contents of /sys/class/backlight
total 0
lrwxrwxrwx 1 root root 0 Jan  9 00:49 amdgpu_bl1 ->
../../devices/pci0000:00/0000:00:08.1/0000:06:00.0/backlight/amdgpu_bl1/

this is the content on 6.0.12
total 0
lrwxrwxrwx 1 root root 0 Jan  8 20:59 amdgpu_bl1 ->
../../devices/pci0000:00/0000:00:08.1/0000:06:00.0/backlight/amdgpu_bl1/
lrwxrwxrwx 1 root root 0 Jan  8 20:59 nvidia_wmi_ec_backlight ->
../../devices/pci0000:00/PNP0C14:00/wmi_bus/wmi_bus-PNP0C14:00/603E9613-EF25-4338-A3D0-C46177516DB7/backlight/nvidia_wmi_ec_backlight/

Distro: Endeavour OS
Kernel: 6.1.4-arch1-1
GPU: RTX 3060 Using nvidia proprietary drivers version 525.78.01

#regzbot introduced v6.1..v6.1.4