dma-mapping: mark DMA_nBITS_MASK as deprecated

Mark them deprecated so that out-of-tree developers get notified about
this before their modules break when these macros are removed.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Yang Hongyang <yanghy@cn.fujitsu.com>
Acked-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>