drm/i915/vrr: Make helpers for cmrr and vrr timings

Separate out functions for computing cmrr and vrr timings.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250311093751.1329043-4-ankit.k.nautiyal@intel.com