drm/i915/cdclk: Rework bw_min_cdclk handling

drm/i915/cdclk: Rework bw_min_cdclk handling

Update bw_min_cdclk directly from intel_bw_calc_min_cdclk()
rather than doing it later from intel_compute_min_cdclk().
This will allow better control over when to update the
cdclk. For now we preserve the current behaviour by allowing
the cdclk to decrease when any pipe needs to do a full modeset.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250923171943.7319-12-ville.syrjala@linux.intel.com
Reviewed-by: Mika Kahola <mika.kahola@intel.com>