checkpatch: Add test for assignment at start of line

Kernel style seems to prefer line wrapping an assignment with the assignment operator on the previous line like:

	<leading tabs>	identifier =
				expression;
over
	<leading tabs>	identifier
				= expression;

somewhere around a 50:1 ratio

$ git grep -P "[^=]=\s*$" -- "*.[ch]" | wc -l
52008
$ git grep -P "^\s+[\*\/\+\|\%\-]?=[^=>]" | wc -l
1161

So add a --strict test for that condition.

---
 scripts/checkpatch.pl | 6 ++++++
 1 file changed, 6 insertions(+)

index 5fe361e1ed5e..af2b73f19605 100755
@@ -3062,6 +3062,12 @@ sub process {
 			}
 		}
 
+# check for assignments on the start of a line
+		if ($sline =~ /^\+\s+($Assignment)[^=]/) {
+			CHK("ASSIGNMENT_CONTINUATIONS",
+			    "Assignment operator '$1' should be on the previous line\n" . $hereprev);
+		}
+
 # check for && or || at the start of a line
 		if ($rawline =~ /^\+\s*(&&|\|\|)/) {
 			CHK("LOGICAL_CONTINUATIONS",