drm/radeon: Use TTM builtin resource manager debugfs code

Switch to using the TTM resource manager debugfs helpers. The
functionality is largely the same.
The TTM resource managers need to stay valid for as long as the
drm debugfs_root is valid.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20220412033526.369115-6-zack@kde.org
Reviewed-by: Christian König <christian.koenig@amd.com>