drm/ttm: flip over the sys manager to self allocated nodes

Make sure to allocate a resource object here.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210602100914.46246-3-christian.koenig@amd.com