Link tools and tests against libfdt shared library

Currently the libfdt based tools (fdtput, fdtget, etc.) and all the
test binaries using libfdt are linked against the static version of libfdt.
That's made it very easy in the past to forget to properly update the
version.lds file which is needed to make functions publicaly accessible
from the shared library.

To avoid problems like that in future, alter the build so that we link and
run the tests against the shared library version of libfdt.

That immediately points out several important symbols that are still
missing from the version.lds, so fix those as well.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>