drm/i915/display: Avoid use of VTOTAL.Vtotal bits

For platforms that always use VRR Timing Generator, the VTOTAL.Vtotal
bits are not required. Since the support for these bits is going to
be deprecated in upcoming platforms, avoid writing these bits for the
platforms that do not use legacy Timing Generator.

Since for these platforms vrr.vmin is always filled with crtc_vtotal,
use TRAN_VRR_VMIN to get the vtotal for adjusted_mode.

v2: Avoid having a helper for manipulating VTOTAL register, and instead
just make the change where required. (Ville)
v3: Set crtc_vtotal instead of working with the bits directly (Ville).
Use intel_vrr_vmin_vtotal() to set the vtotal during readout. (Ville)
v4: Keep the reading part unchanged, and let it get overwritten for
cases where we use vrr.vmin. (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/20250327144629.648306-3-ankit.k.nautiyal@intel.com