editorconfig: new file

Add an editorconfig file so editors can figure out that the *.inc files
should be indented with tabs. At least neovim would use spaces
otherwise.

Change-Id: I93f8fa0c1f2721d12183f33f4a14e13b2deed80b

.editorconfig

@@ -0,0 +1,13 @@
+; This file is for unifying the coding style for different editors and IDEs.
+; See http://editorconfig.org for details.
+
+# Top-most EditorConfig file.
+root = true
+
+[build/*.inc]
+indent_size = 8
+indent_style = tab
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+