drm: Fix kerneldoc for drm_mm_scan_remove_block()

The nodes must be removed in the *reverse* order. This is correct in the
overview, but backwards in the function description. Whilst here add
Intel's copyright statement and tweak some formatting.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161222083641.2691-23-chris@chris-wilson.co.uk