feat(stm32mp2): add RETRAM map/unmap capability

Add RETRAM base address and size definition at platform level.
RETRAM is used by the DDR driver to store retention registers (DDR
training results) in order to restore them in standby exit sequence.
Add map/unmap services at platform level and configure dedicated RISAB5.

Signed-off-by: Nicolas Le Bayon <nicolas.le.bayon@st.com>
Signed-off-by: Maxime Méré <maxime.mere@foss.st.com>
Change-Id: I460b36fccce62e83c1fbff298f96b23530aaa4f3
4 files changed