configure: Check for libfdt version 1.4.0

Some recent patches require a function from libfdt version 1.4.0,
so we should check for this version during the configure step
already. Unfortunately, there does not seem to be a proper #define
for the version number in the libfdt headers. So alternatively,
we check for the availability of the required function
fdt_get_property_by_offset() instead instead.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alexander Graf <agraf@suse.de>

configure

@@ -3115,9 +3115,11 @@ fi
 if test "$fdt" != "no" ; then
   fdt_libs="-lfdt"
   # explicitly check for libfdt_env.h as it is missing in some stable installs
+  # and test for required functions to make sure we are on a version >= 1.4.0
   cat > $TMPC << EOF
+#include <libfdt.h>
 #include <libfdt_env.h>
-int main(void) { return 0; }
+int main(void) { fdt_get_property_by_offset(0, 0, 0); return 0; }
 EOF
   if compile_prog "" "$fdt_libs" ; then
     # system DTC is good - use it
@@ -3135,7 +3137,7 @@ EOF
     fdt_libs="-L\$(BUILD_DIR)/dtc/libfdt $fdt_libs"
   elif test "$fdt" = "yes" ; then
     # have neither and want - prompt for system/submodule install
-    error_exit "DTC (libfdt) not present. Your options:" \
+    error_exit "DTC (libfdt) version >= 1.4.0 not present. Your options:" \
         "  (1) Preferred: Install the DTC (libfdt) devel package" \
         "  (2) Fetch the DTC submodule, using:" \
         "      git submodule update --init dtc"