realtek: add support for port led configuration on RTL93XX

realtek: add support for port led configuration on RTL93XX

Using the led-set attribute of a port in the dts we allow configuration
of the port leds. Each led-set is being defined in the led-set configuration
of the .dts, giving a specific configuration to steer the port LEDs via a serial
connection.

Signed-off-by: Birger Koblitz <git@birger-koblitz.de>