drm/i915/dmc: Limit pipe DMC clock gating w/a to just ADL/DG2/MTL

drm/i915/dmc: Limit pipe DMC clock gating w/a to just ADL/DG2/MTL

Supposedly nothing post-MTL (even BMG) needs the pipe DMC clock
gating w/a (Wa_16015201720), so don't apply it.

TODO: check if the ADL/DG2 "clock gating needed during DMC loading" part
      is actually needed, not seeing anything in the docs about it...

Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250617170759.19552-2-ville.syrjala@linux.intel.com