linux/kernel.h: add/correct kernel-doc notation

Add kernel-doc notation for some macros.  Correct kernel-doc comments &
typos for a few macros.

Link: http://lkml.kernel.org/r/76fa1403-1511-be4c-e9c4-456b43edfad3@infradead.org


Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>