ARM: dts: stm32: Replace SAI format with dai-format DT property

The dai-format and format are handled equally by sound-core.c , the
later is however the only documented property in audio-graph-port.yaml .
Switch to the later.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Olivier Moysan <olivier.moysan@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>