ARM: dts: Add thermistor dts fragment used by exynos based Peach boards

This patch creates a thermistor fragment carrying the NTC
Thermistor nodes as children of the IIO based ADC.

This fragment is included in exynos5420-peach-pit.dts and
exynos5800-peach-pi.dts.

Signed-off-by: Naveen Krishna Chatradhi <ch.naveen@samsung.com>
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>