ARM: dts: stm32: Auto-detect DHSOM with uSD level translator

The uSD level translator on DHSOM and Avenger96 are optional, however it
is possible to auto-detect it. This is done by setting SD CMD line high,
and then testing whether signal level on CK line matches the signal level
on CKIN line. If so, the uSD level translator is present, otherwise it is
not populated.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>