stm32mp: stm32prog: add MMC device

Add support of MMC device (based on DFU_MMC backend)
for SD card and eMMC update.

Create a GPT partitioning on the device.

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