USB: ohci: da8xx: Add devicetree bindings

This patch documents the device tree bindings required for
the ohci controller found in TI da8xx family of SoC's

Cc: robh+dt@kernel.org
Cc: mark.rutland@arm.com
Cc: devicetree@vger.kernel.org
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Axel Haslam <ahaslam@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>