drm/armada: Remove armada_drm_debugfs_cleanup()

drm_debugfs_cleanup() now removes all minor->debugfs_list entries
automatically, so no need to do this explicitly. Additionally it
uses debugfs_remove_recursive() to clean up the debugfs files,
so no need for adding fake drm_info_node entries.
And finally there's no need to clean up on error,
drm_debugfs_cleanup() is called in the error path.

Cc: linux@armlinux.org.uk
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170126225621.12314-6-noralf@tronnes.org