Add kernel-doc function headers in kernel/dma.c and use it in DocBook.

Clean up kernel-doc in mca_dma.h (the colon (':') represents a
section header).
Signed-off-by: NRandy Dunlap <rdunlap@xenotime.net>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>