Update dtc submodule to v1.4.3

Since the last submodule update (which was v1.4.2) dtc and libfdt have
gained some features which would be useful in qemu.  There's now a v1.4.3
upstream release, so update our submodule to point to it.

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

diff --git a/dtc b/dtc
index ec02b34c05be04f249ffaaca4b666f5246877dea..fa8bc7f928ac25f23532afc8beb2073efc8fb063 160000 (submodule)
--- a/dtc
+++ b/dtc
@@ -1 +1 @@
-Subproject commit ec02b34c05be04f249ffaaca4b666f5246877dea
+Subproject commit fa8bc7f928ac25f23532afc8beb2073efc8fb063