ARM: dts: add 'dr_mode' property to hsotg devices for exynos boards

All currently supported boards use hsotg/dwc2 controller in device
('peripheral') mode, so add property which sets correct operation mode.
This patch fixes support in recent changes in dwc2 driver, which added
support for dual-role devices.

Suggested-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>