drm/i915: Move M/N setup to a more logical place on ddi platforms

Let's do the cpu transcoder M/N setup next to where we program
most other cpu transcoder timings/etc.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220128103757.22461-9-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>