drm/ttm/ttm_bo: Fix one function header - demote lots of kernel-doc abuses

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/ttm/ttm_bo.c:51: warning: Function parameter or member 'ttm_global_mutex' not described in 'DEFINE_MUTEX'
 drivers/gpu/drm/ttm/ttm_bo.c:286: warning: Function parameter or member 'bo' not described in 'ttm_bo_cleanup_memtype_use'
 drivers/gpu/drm/ttm/ttm_bo.c:359: warning: Function parameter or member 'bo' not described in 'ttm_bo_cleanup_refs'
 drivers/gpu/drm/ttm/ttm_bo.c:359: warning: Function parameter or member 'interruptible' not described in 'ttm_bo_cleanup_refs'
 drivers/gpu/drm/ttm/ttm_bo.c:359: warning: Function parameter or member 'no_wait_gpu' not described in 'ttm_bo_cleanup_refs'
 drivers/gpu/drm/ttm/ttm_bo.c:359: warning: Function parameter or member 'unlock_resv' not described in 'ttm_bo_cleanup_refs'
 drivers/gpu/drm/ttm/ttm_bo.c:424: warning: Function parameter or member 'bdev' not described in 'ttm_bo_delayed_delete'
 drivers/gpu/drm/ttm/ttm_bo.c:424: warning: Function parameter or member 'remove_all' not described in 'ttm_bo_delayed_delete'
 drivers/gpu/drm/ttm/ttm_bo.c:635: warning: Function parameter or member 'bo' not described in 'ttm_bo_evict_swapout_allowable'
 drivers/gpu/drm/ttm/ttm_bo.c:635: warning: Function parameter or member 'ctx' not described in 'ttm_bo_evict_swapout_allowable'
 drivers/gpu/drm/ttm/ttm_bo.c:635: warning: Function parameter or member 'locked' not described in 'ttm_bo_evict_swapout_allowable'
 drivers/gpu/drm/ttm/ttm_bo.c:635: warning: Function parameter or member 'busy' not described in 'ttm_bo_evict_swapout_allowable'
 drivers/gpu/drm/ttm/ttm_bo.c:769: warning: Function parameter or member 'bo' not described in 'ttm_bo_add_move_fence'
 drivers/gpu/drm/ttm/ttm_bo.c:769: warning: Function parameter or member 'man' not described in 'ttm_bo_add_move_fence'
 drivers/gpu/drm/ttm/ttm_bo.c:769: warning: Function parameter or member 'mem' not described in 'ttm_bo_add_move_fence'
 drivers/gpu/drm/ttm/ttm_bo.c:769: warning: Function parameter or member 'no_wait_gpu' not described in 'ttm_bo_add_move_fence'
 drivers/gpu/drm/ttm/ttm_bo.c:806: warning: Function parameter or member 'bo' not described in 'ttm_bo_mem_force_space'
 drivers/gpu/drm/ttm/ttm_bo.c:806: warning: Function parameter or member 'place' not described in 'ttm_bo_mem_force_space'
 drivers/gpu/drm/ttm/ttm_bo.c:806: warning: Function parameter or member 'mem' not described in 'ttm_bo_mem_force_space'
 drivers/gpu/drm/ttm/ttm_bo.c:806: warning: Function parameter or member 'ctx' not described in 'ttm_bo_mem_force_space'
 drivers/gpu/drm/ttm/ttm_bo.c:872: warning: Function parameter or member 'bo' not described in 'ttm_bo_mem_space'
 drivers/gpu/drm/ttm/ttm_bo.c:872: warning: Function parameter or member 'placement' not described in 'ttm_bo_mem_space'
 drivers/gpu/drm/ttm/ttm_bo.c:872: warning: Function parameter or member 'mem' not described in 'ttm_bo_mem_space'
 drivers/gpu/drm/ttm/ttm_bo.c:872: warning: Function parameter or member 'ctx' not described in 'ttm_bo_mem_space'
 drivers/gpu/drm/ttm/ttm_bo.c:1387: warning: Function parameter or member 'ctx' not described in 'ttm_bo_swapout'

Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: Christian Koenig <christian.koenig@amd.com>
Cc: Huang Rui <ray.huang@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201116174112.1833368-32-lee.jones@linaro.org