drm/i915/display: do not use cursor size reduction on MTL

Cursor size reduction is not supported since MTL.

Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231124-cur_size_reduction-v1-1-30495dba475f@intel.com