Allow Python packages to be dropped

When building in a portage chroot, we do not have the environment needed
to build pylibfdt. It is instead build as a separate package.

Provide a build option to tell U-Boot to skip this part of the build. We
still need it to use binman, etc. but don't need it to build its
dependencies.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
[s/build bytes/builds bytes in tools.rst]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/Makefile b/Makefile
index 9be24c4..efbaf43 100644
--- a/Makefile
+++ b/Makefile
@@ -485,6 +485,15 @@
 export RCS_TAR_IGNORE := --exclude SCCS --exclude BitKeeper --exclude .svn \
 			 --exclude CVS --exclude .pc --exclude .hg --exclude .git
 
+export PYTHON_ENABLE
+
+# This is y if U-Boot should not build any Python tools or libraries. Typically
+# you would need to set this if those tools/libraries (typically binman and
+# pylibfdt) cannot be built by your environment and are provided separately.
+ifeq ($(NO_PYTHON),)
+PYTHON_ENABLE=y
+endif
+
 # ===========================================================================
 # Rules shared between *config targets and build targets