drm/i915: Extract intel_crtc_active_timings()

Declutter intel_crtc_update_active_timings() a bit by
moving the code that determines the timings into a separate
function.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241210211007.5976-12-ville.syrjala@linux.intel.com


Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>