checkpatch: add test for SPDX-License-Identifier on wrong line #

Warn when any SPDX-License-Identifier: tag is not created on the proper
line number.

Link: http://lkml.kernel.org/r/9b74ee87f8c1b8fd310e213fcb4994d58610fcb6.camel@perches.com
Signed-off-by: Joe Perches <joe@perches.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: "Enrico Weigelt, metux IT consult" <lkml@metux.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>