LoongArch: dts: Add I2S support to Loongson-2K2000

The module is supported, adding it.

Not all Loongson-2K1000 boards have an i2s interface, here is an example
of enabling it:

sound {
	compatible = "loongson,ls-audio-card";
	model = "Loongson-ASoC";
	mclk-fs = <512>;

	cpu {
		sound-dai = <&i2s>;
	};

	codec {
		sound-dai = <&es8323>;
	};
};

&i2c1 {
	status = "okay";
	#address-cells = <1>;
	#size-cells = <0>;

	es8323:es8323@10 {
		compatible = "everest,es8323";
		reg = <0x10>;
		#sound-dai-cells = <0>;
	};
};

&i2s {
	status = "okay";

	clock-frequency = <175000000>;
	#sound-dai-cells = <0>;
};

Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>