editorconfig: leave patch files alone wrt trainling spaces

It is perfectly valid for a patch file to have trailing spaces, when for
example an empty or space-only line is appears in a hunk: if the line if
part of the context, whether it be empty or with only spaces, there will
aways be the leading space introduced by the patch itsef, making for a
sapce-only line; if the line is space-only and removed (or added) that
will also appear as a space-only line.

Currently, our editorconfig wants to unconditionally drop trailing
spaces, so when one edits a patch file to add their SoB and Upstream
tags, such a patch would get badly mangled and would not apply, causing
quite some grief and questioning (sad experience looming in the recent
past here)...

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit 85736a27c8cdddcc65ff769852fde60834f302c7)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

.editorconfig

@@ -29,6 +29,9 @@ indent_size = tab
 indent_style = tab
 indent_size = tab
 
+[*.patch]
+trim_trailing_whitespace = false
+
 [S{0..9}{0..9}*]
 indent_style = tab
 indent_size = tab