Create a library file for libfdt

TF Makefile was linking all the objects files generated for the
fdt library instead of creating a static library that could be
used in the linking stage.

Change-Id: If3705bba188ec39e1fbf2322a7f2a9a941e1b90d
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>
diff --git a/lib/libfdt/libfdt.mk b/lib/libfdt/libfdt.mk
index d03dde2..1cbbd78 100644
--- a/lib/libfdt/libfdt.mk
+++ b/lib/libfdt/libfdt.mk
@@ -15,3 +15,5 @@
 			fdt_wip.c)			\
 
 INCLUDES	+=	-Iinclude/lib/libfdt
+
+$(eval $(call MAKE_LIB,fdt))