Kirkwood: Add support for 6282 based QNAP devices

Add support for the QNAP NAS devices based on Marvell's 6282 Kirkwood
chip (TS-119P+, TS-219P+ and TS-419P+).  The differences to the 6281
based devices are:
 - Ethernet PHY address
 - GPIOs used for buttons (TS-119P+/TS-219P+)

Signed-off-by: Martin Michlmayr <tbm@cyrius.com>
Acked-by: Saeed Bishara <saeed.bishara@gmail.com>
Signed-off-by: Nicolas Pitre <nico@fluxnic.net>