stm32mp1: dynamically build DFU_ALT_INFO

This patch reduces the stm32mp1 environment size and
builds dynamically the DFU board configuration with gpt
and mtd partitions and information from defconfig
(CONFIG_DFU_ALT_RAM0).

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/board/st/common/Kconfig b/board/st/common/Kconfig
index af01ca4..08df845 100644
--- a/board/st/common/Kconfig
+++ b/board/st/common/Kconfig
@@ -5,3 +5,10 @@
 	help
 	  This compile the stboard command to
 	  read and write the board in the OTP.
+
+config DFU_ALT_RAM0
+	string "dfu for ram0"
+	default "uImage ram 0xc2000000 0x2000000;devicetree.dtb ram 0xc4000000 0x100000;uramdisk.image.gz ram 0xc4400000 0x10000000"
+	depends on ARCH_STM32MP && SET_DFU_ALT_INFO
+	help
+	  This defines the partitions of ram used to build dfu dynamically.