drm/i915/cnl: Removing missing DDI_E bits from CNL.

DDI_E is not supported on CNL-U and CNL-Y

When adding the initial support we noticed DDI_E wasn't supported
and removed it on v4 and v5 of that patch.
However for some reason I missed or put back these 2 chunks.

Time to clean it up to avoid later confusion.

Fixes: 8bcd3dd4

 ("drm/i915/cnl: Add power wells for CNL")
Cc: Clint Taylor <clinton.a.taylor@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170808193237.17410-1-rodrigo.vivi@intel.com