gitignore: add intermediates from libfdt build

Since ee95d10b (fdt: Build the new python libfdt module), a number of
additional files are auto-generated/installed into the tools directory.
List these in .gitignore to suppress having them listed as untracked.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
References: ee95d10b (fdt: Build the new python libfdt module)
Reviewed-by: Simon Glass <sjg@chromium.org>

.gitignore

@@ -57,6 +57,14 @@ fit-dtb.blob
 /include/config/
 /include/generated/
 
+# Since "ee95d10 fdt: Build the new python libfdt module", a number of
+# build artifacts and intermediated from the python libfdt module are
+# installed into the /tools directory.
+/tools/_libfdt.so
+/tools/libfdt.py
+/tools/libfdt.pyc
+/tools/libfdt_wrap.c
+
 # stgit generated dirs
 patches-*
 .stgit-edit.txt