dt-bindings: usb: Add RK3588 EHCI

Add compatible for RK3588 EHCI. As far as I know it's fully
compatible with generic-ehci.
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20230522162937.53190-3-sebastian.reichel@collabora.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/generic-ehci.yaml

@@ -61,6 +61,7 @@ properties:
               - ibm,476gtr-ehci
               - nxp,lpc1850-ehci
               - qca,ar7100-ehci
+              - rockchip,rk3588-ehci
               - snps,hsdk-v1.0-ehci
               - socionext,uniphier-ehci
           - const: generic-ehci