feat(libfdt): upgrade libfdt source files

Update the libfdt source files to the upstream commit e37c256 [1].

[1] https://github.com/dgibson/dtc/commit/e37c256

Change-Id: I00e29b467ff6f8c094f68245232a7cedeaa14aef
Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
diff --git a/lib/libfdt/fdt_sw.c b/lib/libfdt/fdt_sw.c
index 68b543c..4c569ee 100644
--- a/lib/libfdt/fdt_sw.c
+++ b/lib/libfdt/fdt_sw.c
@@ -377,7 +377,7 @@
 	fdt_set_totalsize(fdt, newstroffset + fdt_size_dt_strings(fdt));
 
 	/* And fix up fields that were keeping intermediate state. */
-	fdt_set_last_comp_version(fdt, FDT_FIRST_SUPPORTED_VERSION);
+	fdt_set_last_comp_version(fdt, FDT_LAST_COMPATIBLE_VERSION);
 	fdt_set_magic(fdt, FDT_MAGIC);
 
 	return 0;