ARM: dts: Add temperature sensor to exynos5250-spring

Spotted in the Chrome OS 3.8 based device tree.
Needs CONFIG_SENSORS_LM90.

Signed-off-by: Andreas Faerber <afaerber@suse.de>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>