ASoC: fsi: Add missing properties to DT bindings

make dtbs_check:

    arch/arm/boot/dts/r8a7740-armadillo800eva.dt.yaml: sound@fe1f0000: '#sound-dai-cells', 'clocks', 'power-domains' do not match any of the regexes: 'pinctrl-[0-9]+'

Fix this by documenting the missing properties.
Update the example to match reality.
While at it, improve the document title, and comment the various
compatible values with the corresponding SoC names.

Fixes: 2f52475b ("ASoC: fsi: switch to yaml base Documentation")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>