drm/i915: don't apply Display WAs 1125 and 1126 to GLK/CNL+

BSpec does not show these WAs as applicable to GLK, and for CNL it
only shows them applicable for a super early pre-production stepping
we shouldn't be caring about anymore. Remove these so we can avoid
them on ICL too.

v2: Change how we check for gen9 display platforms (Ville).

Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181114012432.21809-1-paulo.r.zanoni@intel.com