evb-rk3399: deduced the dram node size when space reserved

The size dram node need to be deduced by the same amount of reserved space.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>

board/rockchip/evb_rk3399/evb-rk3399.c

@@ -71,5 +71,5 @@ void dram_init_banksize(void)
 {
 	/* Reserve 0x200000 for ATF bl31 */
 	gd->bd->bi_dram[0].start = 0x200000;
-	gd->bd->bi_dram[0].size = 0x80000000;
+	gd->bd->bi_dram[0].size = 0x7e000000;
 }