drm/atmel: Drop drm_vblank_cleanup

Again almost correct, but since interrupts are shut down after vblank
still a race. Proper cleanup would call drm_atomic_helper_shutdown to
make sure this really is safe.

v2: Remove misplace malidp hunk (Liviu).

Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170524145212.27837-18-daniel.vetter@ffwll.ch