drm/tilcdc: Remove tilcdc_debugfs_cleanup()

drm_debugfs_cleanup() now removes all minor->debugfs_list entries
automatically, so the drm_driver.debugfs_cleanup callback is not
needed. Also remove the unused tilcdc_module_ops.debugfs_cleanup()
callback. drm_debugfs_cleanup() removes all debugfs files using
debugfs_remove_recursive(), so there should be no need for such a
callback in the future.

Cc: jsarha@ti.com
Cc: tomi.valkeinen@ti.com
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170126225621.12314-16-noralf@tronnes.org