ARM: dts: Add ISL29018 sensor for exynos based Peach boards

The Exynos5420 based Peach Pit and the Exynos5800 based Peach Pi
machines have an i2c ISL29018 light sensor. This patch adds the
device nodes needed to support this device.

These DTS snippets were taken from the downstream Chrome OS 3.8
kernel Device Tree for Peach Pit and Pi boards.

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>