ARM: mvebu: Add thermal support to Armada XP device tree

This patch adds support for the thermal controller available in
all Armada XP boards. This controller has two 4-byte registers:
one to read the thermal sensor, the other for sensor initialization.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>