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
diff --git a/plat/st/stm32mp2/stm32mp2_private.c b/plat/st/stm32mp2/stm32mp2_private.c
index d33fa0b..a37de56 100644
--- a/plat/st/stm32mp2/stm32mp2_private.c
+++ b/plat/st/stm32mp2/stm32mp2_private.c
@@ -71,6 +71,19 @@
 	enable_mmu_el3(0);
 }
 
+int stm32mp_map_retram(void)
+{
+	return  mmap_add_dynamic_region(RETRAM_BASE, RETRAM_BASE,
+					RETRAM_SIZE,
+					MT_RW | MT_SECURE);
+}
+
+int stm32mp_unmap_retram(void)
+{
+	return  mmap_remove_dynamic_region(RETRAM_BASE,
+					   RETRAM_SIZE);
+}
+
 uintptr_t stm32_get_gpio_bank_base(unsigned int bank)
 {
 	if (bank == GPIO_BANK_Z) {