checkpatch.pl: add "prefer __packed" check

There's a __packed #define for __attribute__((packed)).  Add a checkpatch
to tell people about it.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -2743,6 +2743,11 @@ sub process {
 			WARN("plain inline is preferred over $1\n" . $herecurr);
 		}
 
+# Check for __attribute__ packed, prefer __packed
+		if ($line =~ /\b__attribute__\s*\(\s*\(.*\bpacked\b/) {
+			WARN("__packed is preferred over __attribute__((packed))\n" . $herecurr);
+		}
+
 # check for sizeof(&)
 		if ($line =~ /\bsizeof\s*\(\s*\&/) {
 			WARN("sizeof(& should be avoided\n" . $herecurr);