drm/i915/vrr: s/intel_vrr_compute_config_late/intel_vrr_compute_guardband

drm/i915/vrr: s/intel_vrr_compute_config_late/intel_vrr_compute_guardband

The helper intel_vrr_compute_config_late() practically just computes the
guardband. Rename intel_vrr_compute_config_late() to
intel_vrr_compute_guardband().

Since we are going to compute the guardband and then move the
vblank_start for optmizing guardband move it to
intel_crtc_compute_config() which handles such changes.

v2: Move the function at the last after clocks, pipe_mode etc. are all
    set. (Ville)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/20251016055415.2101347-4-ankit.k.nautiyal@intel.com