stm32mp: stm32prog: add upport of partial update

Add support of partial update, update only some partitions,
and check the coherence of the layout with the existing GPT
partitions (offset and size).

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>