rk3399_common: setup fdtoverlay_addr_r value

fdtoverlay (pxe_utils) require define fdtoverlay_addr_r env variable
for example sunxi-common.h meson64.h already have it.

Signed-off-by: Artem Lapkin <art@khadas.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/include/configs/rk3399_common.h b/include/configs/rk3399_common.h
index b37ed5c..6d710da 100644
--- a/include/configs/rk3399_common.h
+++ b/include/configs/rk3399_common.h
@@ -51,6 +51,7 @@
 	"script_size_f=0x2000\0" \
 	"pxefile_addr_r=0x00600000\0" \
 	"fdt_addr_r=0x01f00000\0" \
+	"fdtoverlay_addr_r=0x02000000\0" \
 	"kernel_addr_r=0x02080000\0" \
 	"ramdisk_addr_r=0x06000000\0" \
 	"kernel_comp_addr_r=0x08000000\0" \