ARM: dts: Fix power off method for exynos5422-odroidxu3-common

The Odroid XU3 family boards have ACOKB pin of PMIC grounded, instead of
pulled up as usual. This means that PMIC must manually set PWRHOLD field
in its CTRL1 register to low before initiating power down.

This fixes Odroid XU3 powering off:
[   25.966053] reboot: Power down
[   25.967679] Power down.
[   26.070174] Power down failed, please power off system manually.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski.k@gmail.com>
Reported-by: Anand Moon <linux.amoon@gmail.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>