ASoC: dt-binding: Add bindings for Allwinner A64 codec's analog path controls

The internal codec on Allwinner A64 is split into 2 parts. The
analog path controls are routed through an embedded custom register
bus accessed through the PRCM block just as on A23/A33/H3.

Add a binding for this hardware.

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Mark Brown <broonie@kernel.org>