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/scripts/dtc/Makefile b/scripts/dtc/Makefile
index 2a48022..f4a16ed 100644
--- a/scripts/dtc/Makefile
+++ b/scripts/dtc/Makefile
@@ -29,3 +29,6 @@
 
 # generated files need to be cleaned explicitly
 clean-files	:= dtc-lexer.lex.c dtc-parser.tab.c dtc-parser.tab.h
+
+# Added for U-Boot
+subdir-y += pylibfdt