board: stm32: use bi_dram[0].start instead of hardcoded value

Use gd->bd->bi_dram[0].start initialized from DT instead of using
hardcoded CONFIG_SYS_SDRAM_BASE from config file.

Remove unused CONFIG_SYS_RAM_BASE and CONFIG_SYS_SDRAM_BASE defines.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/board/st/stm32f429-discovery/stm32f429-discovery.c b/board/st/stm32f429-discovery/stm32f429-discovery.c
index e800d70..500dc5f 100644
--- a/board/st/stm32f429-discovery/stm32f429-discovery.c
+++ b/board/st/stm32f429-discovery/stm32f429-discovery.c
@@ -54,7 +54,7 @@
 
 int board_init(void)
 {
-	gd->bd->bi_boot_params = CONFIG_SYS_SDRAM_BASE + 0x100;
+	gd->bd->bi_boot_params = gd->bd->bi_dram[0].start + 0x100;
 
 	return 0;
 }