drm/i915/cdclk: Indicate whether CDCLK change happens during pre or post plane update

Currently we just get a plain "Changing CDCLK to ..." in the
logs. It would actually be interesting to see whether we're
doing the programming during the pre or post plane phase of
the commit. Include that information in the debug message.

Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240402155016.13733-5-ville.syrjala@linux.intel.com