drm/i915/csr: Added ICL Stepping info

As DMC Package contain DMC FW for multiple steppings including default
stepping. This patch will help to load FW for that particular stepping,
if FW for that stepping is available, instead of loading default FW.

v2 : Fix formatting issue.

Signed-off-by: Jyoti Yadav <jyoti.r.yadav@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1536169347-31326-1-git-send-email-jyoti.r.yadav@intel.com