dt-bindings: mips: realtek: Add rtl930x-soc compatible

Add the rtl9302 SoC and the Cameo RTL9302C_2xRTL8224_2XGE reference
board to the list of Realtek compatible strings.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>