drm/i915/cnl: Extend HDMI 2.0 support to CNL.

Starting on GLK we support HDMI 2.0. So this patch only
extend the work Shashank has made to GLK to CNL.

v2: The version that compiles :/
v3: Invert order to newer || older platforms check. (Ville).

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Shashank Sharma <shashank.sharma@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171115184205.8104-1-rodrigo.vivi@intel.com