cpio: install to /bin and after busybox

As the usual rule consider full-blown packages superior to busybox,
hence build after it.
Also install cpio to /bin to override the busybox-provided one.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>