ARM: dts: stm32: Add QSPI NOR on AV96

The DH Electronics DHCOR SOM has QSPI NOR on the SoM itself, add it
into the DT.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Patrick Delaunay <patrick.delaunay@st.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Patrick Delaunay <patrick.delaunay@st.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Change-Id: Ia7c454c496f50e3fc4851ec1154f3641c416e98e