PROBLEM: EDID regression results in color banding on Lenovo G50 series laptops [fix proposition]

[Tomasz Papież]

Since the introduction of kernel 4.8 I've been experiencing color 
banding on my Lenovo G50-80 notebook. I also had reports of the same 
symptoms on the G50-70 model.

I figured out that the problem had been introduced by commit 
210a021dab639694600450c14b877bf3e3240adc

The G50-80's LCD panel supports 6bpc, but is now set to 8bpc,
and the system probably falls back to 6bpc
without any dithering, which result in heavily banded gradients.

I fixed it for myself by adding an EDID quirk for that particular LCD 
panel (see the attached patch). It's unknown to me, however, if there 
are any other panels affected by the issue, so maybe a more general
solution might be desirable.
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