drm/ttm: rename ttm_bo_put to _fini v3

drm/ttm: rename ttm_bo_put to _fini v3

Give TTM BOs a separate cleanup function.

No funktional change, but the next step in removing the TTM BO reference
counting and replacing it with the GEM object reference counting.

v2: move the code around a bit to make it clearer what's happening
v3: fix nouveau_bo_fini as well

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Acked-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://lore.kernel.org/r/20250909144311.1927-1-christian.koenig@amd.com