meta: Add editor configuration

.editorconfig is supported out-of-the box by many editors (vim, vscode,
etc...). This file prevent new comers to do mistake with their editor
configuration.

Change-Id: I60c3dedc20161883f388af6f1cb9b95b90beff2a
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/9454
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Tested-by: jenkins

.editorconfig

@@ -0,0 +1,17 @@
+# EditorConfig: https://editorconfig.org/
+
+# top-most EditorConfig file
+root = true
+
+# All (Defaults)
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = tab
+indent_size = 4
+tab_width = 4
+
+[*.patch,*.diff]
+trim_trailing_whitespace = false