drm/ttm: drop special pipeline accel cleanup function.

The two accel cleanup paths were mostly the same once refactored.

Just pass a bool to say if the evictions are to be pipelined.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200917064132.148521-2-airlied@gmail.com