drm/i915: Add wrapper for getting display step

Add a wrapper around intel_step_name that takes in driver data as an
argument. This wrapper will help maintain compatibility with the
proposed xe driver.

Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
Signed-off-by: Animesh Manna <animesh.manna@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231003065211.1052385-1-chaitanya.kumar.borah@intel.com