stm32mp: stm32prog: add support of RAM target

stm32mp: stm32prog: add support of RAM target

Add support of RAM target in flashlayout to load kernel image
("system") and device tree ("filesystem") in DDR with DFU and
start these images.

The flashlayout.tsv is:

-	0x01	fsbl		Binary		none	0x00000000	tf-a.stm32
-	0x03	ssbl		Binary		none	0x00000000	u-boot.stm32
P	0x10	kernel		System		ram0	0xC2000000	uImage.bin
P	0x11	dtb		FileSystem	ram0	0xC4000000	dtb.bin

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