dtc: Don't include libfdt in global LDFLAGS

[Jon Loeliger]

So, like, the other day David Gibson mumbled:
> Remove the uneccessary LDFLAGS from the top-level makefile.  It only
> added libfdt/ to the link path.  dtc doesn't need libfdt at all, and
> the testcases which do, already link libfdt.a by explicit path.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.

jdl