BugLink: http://bugs.launchpad.net/bugs/1609742

Sync with v4.7 and un-revert 280201ac which got fixed upstream.

Also drop two workarounds from 9f81d279:

drm/i915/edp: Add WaKVMNotificationOnConfigChange:bdw
- it's only for BDW which doesn't use i915_bpo

drm/i915/skl: Add WAC6entrylatency
- it didn't end up in 4.7
Signed-off-by: Timo Aaltonen <timo.aaltonen@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>