pylibfdt: move pylibfdt to scripts/dtc/pylibfdt and refactor makefile

The pylibfdt is used by dtoc (and, indirectly by binman), but there
is no reason why it must be generated in the tools/ directory.

Recently, U-Boot switched over to the bundled DTC, and the directory
structure under scripts/dtc/ now mirrors the upstream DTC project.
So, scripts/dtc/pylibfdt is the best location.

I also rewrote the Makefile in a cleaner Kbuild style.

The scripts from the upstream have been moved as follows:

  lib/libfdt/pylibfdt/setup.py -> scripts/dtc/pylibfdt/setup.py
  lib/libfdt/pylibfdt/libfdt.i -> scripts/dtc/pylibfdt/libfdt.i_shipped

The .i_shipped is coped to .i during building because the .i must be
located in the objtree when we build it out of tree.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/Makefile b/Makefile
index 67f01ad..f94813d 100644
--- a/Makefile
+++ b/Makefile
@@ -1380,7 +1380,7 @@
 	$(call filechk,timestamp.h)
 
 checkbinman: tools
-	@if ! ( echo 'import libfdt' | ( PYTHONPATH=tools $(PYTHON) )); then \
+	@if ! ( echo 'import libfdt' | ( PYTHONPATH=scripts/dtc/pylibfdt $(PYTHON) )); then \
 		echo >&2; \
 		echo >&2 '*** binman needs the Python libfdt library.'; \
 		echo >&2 '*** Either install it on your system, or try:'; \