drm/i915/dsb: Precompute DSB_CHICKEN

Adjust the code that determines the correct DSB_CHICKEN value
to be usable for use within DSB commands themselves. Ie.
precompute it based on our knowledge of what the hardware state
(VRR vs. not mainly) will be at the time of the commit.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240624191032.27333-9-ville.syrjala@linux.intel.com


Reviewed-by: Animesh Manna <animesh.manna@intel.com>