drm/i915: Eliminate IS_MTL_DISPLAY_STEP

Stepping-specific display behavior shouldn't be tied to MTL as a
platform, but rather specifically to the Xe_LPD+ IP.  Future non-MTL
platforms may re-use this IP and will need to follow the exact same
logic and apply the same workarounds.  IS_MTL_DISPLAY_STEP() is dropped
in favor of a new macro IS_DISPLAY_IP_STEP() that only checks the
display IP version.

v2:
 - Rename macro to IS_DISPLAY_IP_STEP for consistency with the
   corresponding GT macro and handle steppings the same way.
v3:
 - Drop the automatic "STEP_" pasting.
v4:
 - Implement IS_DISPLAY_IP_STEP on top of IS_DISPLAY_IP_RANGE /
   IS_DISPLAY_STEP building blocks and make the parameters from/until
   instead of begin/fixed.  (Jani)
 - Fix usage details in comment.
v5:
 - Tweak macro comment.  (Gustavo)

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230821180619.650007-17-matthew.d.roper@intel.com