dt-bindings: renesas,sh-msiof: Add MSIOF I2S Sound support

dt-bindings: renesas,sh-msiof: Add MSIOF I2S Sound support

Renesas MSIOF (Clock-Synchronized Serial Interface with FIFO) can work as
both SPI and I2S. MSIOF-I2S will use Audio Graph Card/Card2 driver which
uses Of-Graph in DT.

MSIOF-SPI/I2S are using same DT compatible properties.
MSIOF-I2S         uses Of-Graph for Audio-Graph-Card/Card2,
MSIOF-SPI doesn't use  Of-Graph.

Adds schema for MSIOF-I2S (= Sound).

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: "Rob Herring (Arm)" <robh@kernel.org>
Link: https://patch.msgid.link/87zfge2x0u.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>