Add limited compatibility for Lenovo X1 Yoga 2nd Gen

[spease]

This does change the screen brightness. A couple of caveats:

• It doesn't work especially well with redshift. I'm not sure how to fix this, or if a proper fix even exists (I suspect it doesn't)
• Although it does dim and brighten the screen, I don't know how to tell if it's calibrated to the correct range. The screen is still somewhat visible at 0% but it is bright at 100%

[jackpot51]

Are all X1 Yoga 2nd Gen systems OLED?

[spease]

No, but I suspect a /sys/class/dmi/id/product_name of 20JES0CS00 will restrict it to the model I have. I looked at reading the EDID information, but it was pretty generic.

$ cat /sys/class/drm/card0-eDP-1/edid | parse-edid
Checksum Correct

Section "Monitor"
        Identifier ""
        ModelName ""
        VendorName "LEN"
        # Monitor Manufactured week 49 of 2015
        # EDID version 1.4
        # Digital Display
        DisplaySize 310 180
        Gamma 2.20
        Option "DPMS" "true"
        Modeline        "Mode 0" 242.19 2560 2608 2640 2720 1440 1443 1449 1484 +hsync -vsync
        Modeline        "Mode 1" 242.19 2560 2608 2640 2720 1440 1443 1449 1484 +hsync -vsync
EndSection

Does the product_name method seem reasonable?

[jackpot51]

Yes, if you can restrict it to that SKU