drm/i915/vrr: Use crtc_vtotal for vmin

To have fixed refresh rate with VRR timing generator the
guardband/pipeline full can't be programmed on the fly. So we need to
ensure that the values satisfy both the fixed and variable refresh
rates.

Since we compute these value based on vmin, lets set the vmin to
crtc_vtotal for both fixed and variable timings instead of using the
current refresh rate based approach. This way the guardband remains
sufficient for both cases.

v2: Avoid using vblank delay while computing vtotal, as this comes into
the picture later. (Ville)

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/20250311093751.1329043-7-ankit.k.nautiyal@intel.com