arm64: dts: allwinner: a64: Remove unused SPDIF sound card

As of v5.7-rc2, Linux now prints the following message at boot:

  [   33.848525] platform sound_spdif: deferred probe pending

This is because sound_spdif is waiting on its CPU DAI &spdif to probe,
but &spdif is disabled in the device tree.

Exposure of the SPDIF pin is board-specific functionality, so the sound
card and codec DAI belong in the individual board DTS, not the SoC DTSI.
In fact, no in-tree A64 board DTS enables &spdif, so let's remove the
card and DAI entirely.

This reverts commit 78e07137

.

Acked-by: Clément Péron <peron.clem@gmail.com>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>