ARM: Kirkwood: Add support thermal sensor for 88F6282 and 88F6283

Kirkwood 88F6282 and 88F6283 have a thermal sensor.
This patch adds a DT node and enables the driver in the kernel config.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>