ARM: dts: Add max77686 device tree support for CROS5250

The exynos5250 based chromebooks have a max77686 pmic on i2c channel 0.
Add support for the pmic in the common cros5250 dts file.
Tested after enabling cpufreq support for exynos5250 SoC and varying the
arm frequency/voltage using the userspace governer.

Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Acked-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>