checkpatch: emit "NOTE: <types>" message only once after multiple files

Make this message similar to the "false positives" message and emit it
only once when scanning multiple files instead of after each file scanned.

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