drm/i915/skl: drop workarounds for F0 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/e5433e6430dcfd941209c4d8103035ddb13d17b4.1474034059.git.jani.nikula@intel.com