ARM: dts: Explicitly set dr_mode on exynos Peach boards

In case the optional dr_mode property isn't set in the dwc3 nodes the
the controller will go into OTG mode if both USB host and USB gadget
functionality are enabled in the kernel configuration. Unfortunately
this results in USB not working on exynos5420-peach-pit and
exynos5800-peach-pi with such a kernel configuration unless manually
change the mode. To resolve that explicitly configure the dual role
mode as host.

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Reviewed-by: Andreas Faerber <afaerber@suse.de>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>