ASoC: dt-bindings: renesas: Fix R-Car Gen4 SoC-specific compatibles

make dtbs_check:

    arch/arm64/boot/dts/renesas/r8a779g0-white-hawk.dtb: sound@ec5a0000: compatible: 'oneOf' conditional failed, one must be fixed:
	    ['renesas,rcar_sound-r8a779g0', 'renesas,rcar_sound-gen4'] is too short
	    ...
	    'renesas,rcar_sound-r8a779h0' was expected

The list of SoC-specific compatible values for R-Car Gen4 SoCs is
mutually-exclusive, just like for other R-Car SoC generations, so it
should use an enum.

Fixes: d6e792ed ("ASoC: dt-bindings: renesas: add R8A779H0 V4M")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/b3a6cf12c46b23a501b0d54c6892b969e2a55145.1713874657.git.geert+renesas@glider.be


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