rockchip: rv1126: Enable fdtoverlay support

Add fdtoverlay_addr_r and enable OF_LIBFDT_OVERLAY for the
use of DT overlay in RV1126.

Signed-off-by: Jagan Teki <jagan@edgeble.ai>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/include/configs/rv1126_common.h b/include/configs/rv1126_common.h
index 1ec1640..a64c0c6 100644
--- a/include/configs/rv1126_common.h
+++ b/include/configs/rv1126_common.h
@@ -24,6 +24,7 @@
 	"scriptaddr=0x00000000\0" \
 	"pxefile_addr_r=0x00100000\0" \
 	"fdt_addr_r=0x08300000\0" \
+	"fdtoverlay_addr_r=0x02000000\0" \
 	"kernel_addr_r=0x02008000\0" \
 	"ramdisk_addr_r=0x0a200000\0"