patman: use -D option for git format-patch

This allows Patman to generate smaller patches for file removal.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Simon Glass <sjg@chromium.org>
Acked-by: Heiko Schocher <hs@denx.de>
diff --git a/tools/patman/gitutil.py b/tools/patman/gitutil.py
index 9e739d8..67b086b 100644
--- a/tools/patman/gitutil.py
+++ b/tools/patman/gitutil.py
@@ -264,7 +264,7 @@
     """
     if series.get('version'):
         version = '%s ' % series['version']
-    cmd = ['git', 'format-patch', '-M', '--signoff']
+    cmd = ['git', 'format-patch', '-D', '-M', '--signoff']
     if series.get('cover'):
         cmd.append('--cover-letter')
     prefix = series.GetPatchPrefix()