drm/ttm: remove ttm_tt_destroy_common v2

Move the functionality into ttm_tt_fini and ttm_bo_tt_destroy instead.

We don't need this any more since we removed the unbind from the destroy
code paths in the drivers.

Also add a warning to ttm_tt_fini() if we try to fini a still populated TT
object.

v2: instead of reverting the patch move the functionality to different
places.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210728130552.2074-5-christian.koenig@amd.com