sandbox: Move to use live tree

This updates sandbox to use a live device tree. This means that after
relocation (from board_init_r() onwards) it no-longer uses flat device
tree.

Signed-off-by: Simon Glass <sjg@chromium.org>

configs/sandbox_defconfig

@@ -62,6 +62,7 @@ CONFIG_CMD_EXT4_WRITE=y
 CONFIG_MAC_PARTITION=y
 CONFIG_AMIGA_PARTITION=y
 CONFIG_OF_CONTROL=y
+CONFIG_OF_LIVE=y
 CONFIG_OF_HOSTFILE=y
 CONFIG_NETCONSOLE=y
 CONFIG_REGMAP=y