drm/xe: Move xe_ttm_sys_mgr_init() downwards.

Now that all previous allocations are gone, ensure no new allocations
will ever be done before xe_display_init_early(), by moving the call
that allows allocations downwards.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20250619104858.418440-21-dev@lankhorst.se


Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>