drm/i915: Invert if/else ladder for stolen init

Continue converting the driver to the convention of last version first,
extending it to the future platforms. Now, any GRAPHICS_VER >= 11 will
be handled by the first branch.

Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220908-if-ladder-v2-3-7a7b15545c93@intel.com
Link: https://patchwork.freedesktop.org/patch/msgid/20220912-copy-engine-v1-1-ef92fd81758d@intel.com