drm/i915: move cdclk_funcs to display.funcs

Move display cdclk functions under drm_i915_private display sub-struct.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/77e12e21bb9682a3c1d54f8d59eecc5945ef16d0.1661346845.git.jani.nikula@intel.com