checkpatch: extend attribute testing to all modifiers

We should allow testing of all modifiers not just attributes.  Extend
testing and test for all the know modifiers.

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