ARM: stm32: Enable assorted ST specific commands on DHSOM

Enable the stm32prog, stm32key, stboard commands on DHSOM.
Those can be used e.g. to implement verified boot.

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