pylibfdt: Allow building to be disabled

Some build systems want to build python libraries separately from the
rest of the build.

Add a NO_PYTHON option to enable this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Makefile

@@ -120,6 +120,7 @@ SCRIPTS = dtdiff
 # We need both Python and swig to build pylibfdt.
 .PHONY: maybe_pylibfdt
 maybe_pylibfdt: FORCE
+	if [ -n "${NO_PYTHON}" ]; then exit; fi; \
 	if $(PKG_CONFIG) --cflags python >/dev/null 2>&1; then \
 		if which swig >/dev/null 2>&1; then \
 			can_build=yes; \

README

@@ -50,6 +50,12 @@ If you add new features, please check code coverage:
     # Open 'htmlcov/index.html' in your browser
 
 
+To disable building the python library, even if swig and Python are available,
+use:
+
+    make NO_PYTHON=1
+
+
 More work remains to support all of libfdt, including access to numeric
 values.