docs(stm32mp1): update doc for FIP/FCONF

Describe the boot using FIP, and how to compile it.
The STM32IMAGE boot chain is still available but it is not recommended.
Update the build command lines, for FIP.
The memory mapping is also updated.

Change-Id: I2b1e0df5500b6213d33dc558b0e0da38340a4d79
Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
1 file changed