sandbox: Move section u_boot_list to make it RW

In order to be able to update data in u_boot_list, move this section to
make it RW.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/cpu/u-boot-spl.lds b/arch/sandbox/cpu/u-boot-spl.lds
index de65b01..c60eb10 100644
--- a/arch/sandbox/cpu/u-boot-spl.lds
+++ b/arch/sandbox/cpu/u-boot-spl.lds
@@ -20,4 +20,4 @@
 	__bss_start = .;
 }
 
-INSERT BEFORE .data;
+INSERT AFTER .data;