drm/i915/cnl: Move ddi buf trans related functions up.

No functional changes. But those functions will be needed
to get max level for HDMI and DP, so let's move those
up closer to other similar functions existent for previous
platforms.

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/20170829232230.23051-6-rodrigo.vivi@intel.com