drm/i915/cdclk: Extract cdclk_divider()

Extract the cdclk divider calculation into a helper. We'll have
more users of this soon. We can now also get rid of the intermediate
'unsquashed_cdclk' variable.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240207013334.29606-2-ville.syrjala@linux.intel.com


Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>