ASoC: dt-bindings: add mclk provider support to stm32 i2s

Add master clock provider support to STM32 I2S.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Link: https://lore.kernel.org/r/20210205104404.18786-2-olivier.moysan@foss.st.com


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