dt-bindings: connector: usb: allow a single HS port

dt-bindings: connector: usb: allow a single HS port

Allow a single HS port to be used e.g. without reg property and a unit
address. OF graph allows a single port node, without 'reg' property.

This removes a couple of Warnings or errors on STM32MP boards.
When using single HS port currently, when doing building with W=1:
arch/arm/boot/dts/stm32mp157c-dk2.dtb: stusb1600@28: connector:
Unevaluated properties are not allowed ('port' was unexpected)

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20230620085633.533187-1-fabrice.gasnier@foss.st.com
Signed-off-by: Rob Herring <robh@kernel.org>