feat(stm32mp1): configure the serial boot load address

For product with 128MB DDR size, the OP-TEE is located at the end
of the DDR and the FIP can't be loaded at the default location
because it overlap the OP-TEE final location. So the default value
for DWL_BUFFER_BASE is invalid.

To avoid this conflict the serial boot load address = DWL_BUFFER_BASE
can be modified with a configuration flags.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Change-Id: Ie27b87c10c57fea5d4c6200ce4f624e775b9a080
diff --git a/plat/st/stm32mp1/platform.mk b/plat/st/stm32mp1/platform.mk
index 7203de8..be07a4b 100644
--- a/plat/st/stm32mp1/platform.mk
+++ b/plat/st/stm32mp1/platform.mk
@@ -121,6 +121,9 @@
 STM32MP_USB_PROGRAMMER	?=	0
 STM32MP_UART_PROGRAMMER	?=	0
 
+# Download load address for serial boot devices
+DWL_BUFFER_BASE 	?=	0xC7000000
+
 # Device tree
 ifeq ($(STM32MP13),1)
 BL2_DTSI		:=	stm32mp13-bl2.dtsi
@@ -225,6 +228,7 @@
 
 $(eval $(call add_defines,\
 	$(sort \
+		DWL_BUFFER_BASE \
 		PLAT_PARTITION_MAX_ENTRIES \
 		PLAT_XLAT_TABLES_DYNAMIC \
 		STM32_TF_A_COPIES \