ASoC: rockchip-i2s: add description for px30

Add "rockchip,px30-i2s", "rockchip,rk3066-i2s" for i2s on px30 platform.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Liang Chen <cl@rock-chips.com>
Signed-off-by: Mark Brown <broonie@kernel.org>