drm/i915: Kill WA 0528

drm/i915: Kill WA 0528

First of all I believe this WA as written here was wrong.

Because it is listed on BSpec only for SKL and BXT, exactly
the only 2 platforms skipped here.

But also it is written there that we don't need this WA
anymore:
"This workaround is no longer needed since NV12 support is
dropped for the affected projects in #0870."

SO, let's kill it.

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Vidya Srinivas <vidya.srinivas@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181031162845.12419-1-rodrigo.vivi@intel.com