ARM: dts: stm32: Repair SDMMC2 operation

The eMMC uses different pinmux for the top four data lines, use such
a pinmux, otherwise it takes a very long time until the test for 8bit
operation times out. And this is the correct pinmux per schematic too.

Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@st.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Patrick Delaunay <patrick.delaunay@st.com>
Cc: Patrice Chotard <patrice.chotard@st.com>