ARM: dts: stm32: Enable SDMMC3 on DH DRC02

The DH DRC02 board has an on-board microSD slot,
add DT properties to enable the slot.

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