drm/i915: Move HAS_L3_DPF definition to platform definition

Moving all GPU features to the platform definition allows for
        - standard place when adding new features from new platforms
        - possible to see supported features when dumping struct
          definitions

Signed-off-by: Carlos Santa <carlos.santa@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>