ASoC: rockchip-i2s: add description for rk3308

The description below is already in use for rk3308.dtsi,
but was somehow never added to a document, so add
"rockchip,rk3308-i2s", "rockchip,rk3066-i2s"
for i2s nodes on a rk3308 platform to rockchip-i2s.yaml.
One of the rk3308 i2s nodes also has a different dma layout,
so change that as well.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Link: https://lore.kernel.org/r/20200507113238.7904-1-jbx6244@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>