drm/i915/skl: drop workarounds for D0 revision

Pre-production hardware is not supported.

Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/d28d21ceddeec226b5d1a20a7382bee9a72709a4.1474034059.git.jani.nikula@intel.com