dt-bindings: usb: Add TI tps6598x device tree binding documentation

dt-bindings: usb: Add TI tps6598x device tree binding documentation

Add device tree binding documentation for the Texas Instruments tps6598x
Type-C chip driver.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Link: https://lore.kernel.org/r/20200507214733.1982696-2-bryan.odonoghue@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>