Fix the libufdt overlay node order

libufdt could reversed the node order during overlaying.

However, the libfdt overlay in dtc doesn't promise the node order.
But looks there are some implementation of kernel drivers depend on
the order in DTS.

The patch keeps the DTB/DTBO node order during libufdt overlaying.
Notes that the node order merged by libufdt could not match the
result of libfdt.

Bug: 35429321
Test: run test scripts (see libufdt/tests/README)
Change-Id: I7209ebfaa21d6640d547b029ea0f0edf6e58fca1