[dtc] breaking out libfdt from dtc so other progs can use it

[Jerone Young <jyoung5@us.ibm.com>]

Currently the dtc source code has libfdt integrated in it. This seems to
have become place for upstream libfdt changes. Now we all know everyone
(linux kernel, cuboot) also have their own versions over libfdt. But if
another userspace app wants to use libfdt , it has to copy it from the
dtc source and try to maintain it's own copy.

The question I have is can libfdt be split out from dtc source, and
become it's own thing. This way other userspace apps can easily download
it and link with it?

The reason I ask is I have added dynamic manipulation support of device
trees in memory into qemu for KVM. But the issue is keeping a copy of
libfdt in the KVM userspace repository, which is getting some opposition
(understandably). But this would be much easier if there was a libfdt
repo for the library so that we wouldn't need to keep our own copy.