checkpatch: add test for blank lines after function/struct/union/enum

Add a --strict test asking for a blank line after
function/struct/union/enum declarations.

Allow exceptions for several attributes and macro uses.

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