EDID/DP color precision fixes on Intel hw for stable (v2)

[Mario Kleiner]

Following Jani's advice, this series just fixes the stable kernel
regressions for DP color precision on Intel by reverting Jani's
commit and adding the edid 6 bpc quirk for the AEO 0 panel to fix
the original fdo bug that triggered this. Minimal patches to allow
easy backporting to affected stable kernels.

I'll send out the patches with improved DP sink precision handling
on top of these in a separate series later, once these have landed.

thanks,
-mario