dt-bindings: usb: hd3ss3220 device tree binding document

Add device tree binding document for TI HD3SS3220 Type-C DRP port
controller driver.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1567584941-13690-2-git-send-email-biju.das@bp.renesas.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>