drm/i915/cfl: Introduce Display workarounds for Coffee Lake.

The whole Display engine for Coffee Lake is pretty much
identical to the Kabylake. For this reason let's reuse
all display related production workardounds here even though
CFL is not explicit listed at Display workarounds page at Spec.

v2: moved intel_pm.c chunck to this patch in order to address
    all display related w/a in a single place.

Cc: Arthur Runyan <arthur.j.runyan@intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1496937000-8450-3-git-send-email-rodrigo.vivi@intel.com