drm/i915: Extract hsw_chicken_trans_reg()

We have the same code to determine the CHICKEN_TRANS register
offset sprinkled in a dozen places. Hoover it up into a small
helper.

TODO: find a better home for this

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231101114212.9345-2-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>