drm/i915/bdw: Add BDW DDI buffer translation values

Many of the DDI buffer translation values have changed for BDW.
Add new translation tables and selection between HSW and BDW.

v2: s/BUG/WARN/ to avoid breaking future GENs.

v3: Rebase on top of the hdmi translation table changes.

v4: Fix up the multiline comment while at it.

Signed-off-by: Art Runyan <arthur.j.runyan@intel.com> (v2)
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>