ASoC: stm32: i2s: add master clock provider

Add master clock generation support in STM32 I2S driver.
The master clock provided by I2S can be used to feed a codec.
Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Link: https://lore.kernel.org/r/20210205104404.18786-3-olivier.moysan@foss.st.comSigned-off-by: Mark Brown <broonie@kernel.org>