[ARM] Kirkwood: Add support for QNAP TS-41x Turbo NAS

Add support for the QNAP TS-410, TS-410U, TS-419P and TS-419U
Turbo NAS.

Signed-off-by: Martin Michlmayr <tbm@cyrius.com>
Signed-off-by: Nicolas Pitre <nico@marvell.com>