drm/i915/cdclk: Remove the assumption that cdclk divider==2 when using squashing

drm/i915/cdclk: Remove the assumption that cdclk divider==2 when using squashing

Currently we have a hardcoded assumption that the cdclk divider
(2*cd2x divider) is always 2 when squashing is used. While that
is true for all current platforms it might not hold in the future.
So eliminate the assumption and calculate the correct divider
from the other parameters.

v2: s/cd2x divider/cdclk divider/ (Gustavo)
    s/clock/unsquashed_cdclk/ (Gustavo)

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/20231211221636.29658-1-ville.syrjala@linux.intel.com