dt-bindings: usb: Convert SMSC USB3503 binding to a schema

The SMSC USB3503 USB Hub Controller is supported by Linux thanks to
its device tree binding.

Now that we have the DT validation in place, let's convert the device
tree bindings for that driver over to a YAML schema.

Cc: Dongjin Kim <tobetter@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20210927073514.14334-1-maxime@cerno.tech


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