drm/i915: Broadwell DDI Buffer translation - more tuning

BDW display - DP buffer translation values changed to give better margin.

Further change to entry 6; set dword 0 bit 31=1.

Both changes were approved already but this one didn't landed BSpec yet
this is why it is in a separated patch. Making reviewer's life easier.
Also alowing separated tests and any future bisect that might be needed.

Reference: Predator r74080 / HSD 4394389

v2: Arthur noticed I was changing the wrong bit.

Cc: Arthur Runyan <arthur.j.runyan@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Arthur Runyan <arthur.j.runyan@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>