drm: Destroy property blobs at mode config cleanup time

Property blob objects need to be destroyed when cleaning up to avoid
memory leaks. Go through the list of all blobs in the
drm_mode_config_cleanup() function and destroy them.

The drm_mode_config_cleanup() function needs to be moved after the
drm_property_destroy_blob() declaration. Move drm_mode_config_init() as
well to keep the functions together.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>