drm/i915/skl: Update DDI buffer translation programming.

SKL-Y can now use the same programming for all VccIO values after an
adjustment to I_boost.  SKL-U DP table adjustments.

1. Remove SKL Y 0.95V from "SKL H and S" columns in all tables. The
   other SKL Y column removes the "0.85V VccIO" so it now applies to all
   voltages.

2. DP table changes SKL U 400mV+0db dword 0 value from 2016h to 201Bh.

3. DP table changes SKL U 600mv+0db dword 0 value from 2016h to 201Bh.

4. DP table increases I_boost to level 3 for SKL Y 400mv+9.5db.

v2: Fix compilation warnings as pointed by Paulo.

Reference: Graphics Spec Change r97962
Cc: Arthur Runyan <arthur.j.runyan@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
[Jani: reformatted commit message for shorter lines.]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>