arm64: dts: rockchip: add the internal audio codec on rk3308

The RK3308 has a built-in audio codec that connects internally to i2s_8ch_2
or i2s_8ch_3.

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Link: https://lore.kernel.org/r/20240305-rk3308-audio-codec-v4-7-312acdbe628f@bootlin.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>