drm/i915/hdmi: Use VRR Timing generator for HDMI for fixed_rr

drm/i915/hdmi: Use VRR Timing generator for HDMI for fixed_rr

Currently VRR is not supported with HDMI, but we can still leverage
the VRR Timing Generator to achieve a fixed refresh rate.
Call intel_vrr_compute_config() for HDMI which will handle the vrr
timings to have fixed refresh rate with VRR Timing Generator.

v2: Improve commit message. (Ville).

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com> (#v1)
Link: https://lore.kernel.org/r/20250324133248.4071909-2-ankit.k.nautiyal@intel.com