ARM: dts: vfxxx: Add iio_hwmon node for ADC temperature channel

Add iio-hwmon node to expose the temperature channel on Vybrid as
hardware monitor device using the iio_hwmon driver.

Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>
Acked-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>