ARM: stm32: Fix OF_LIST on DHCOR

The ITS file used to build the images here lists three dtb files as
being used. Today, these are built by the logic that will over-build dtb
files based on SOC/etc symbols being set. To future proof this platform
and be generally correct, we list all 3 of the device trees used here in
OF_LIST.

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