arm64: dts: rockchip: Switch RK3399-Gru DP to SPDIF output

Commit b18c6c3c ("ASoC: rockchip: cdn-dp sound output use spdif")
switched the platform to SPDIF, but we didn't fix up the device tree.

Drop the pinctrl settings, because the 'spdif_bus' pins are either:
 * unused (on kevin, bob), so the settings is ~harmless
 * used by a different function (on scarlet), which causes probe
   failures (!!)

Fixes: b18c6c3c ("ASoC: rockchip: cdn-dp sound output use spdif")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20220114150129.v2.1.I46f64b00508d9dff34abe1c3e8d2defdab4ea1e5@changeid


Signed-off-by: Heiko Stuebner <heiko@sntech.de>