drivers/dma: remove unused support for MEMSET operations

There have never been any real users of MEMSET operations since they
have been introduced in January 2007 by commit 7405f74bad ("dmaengine:
refactor dmaengine around dma_async_tx_descriptor").  Therefore remove
support for them for now, it can be always brought back when needed.

[sebastian.hesselbarth@gmail.com: fix drivers/dma/mv_xor]
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Cc: Vinod Koul <vinod.koul@intel.com>
Acked-by: Dan Williams <djbw@fb.com>
Cc: Tomasz Figa <t.figa@samsung.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Olof Johansson <olof@lixom.net>
Cc: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/crypto/async-tx-api.txt

@@ -222,5 +222,4 @@ drivers/dma/: location for offload engine drivers
 include/linux/async_tx.h: core header file for the async_tx api
 crypto/async_tx/async_tx.c: async_tx interface to dmaengine and common code
 crypto/async_tx/async_memcpy.c: copy offload
-crypto/async_tx/async_memset.c: memory fill offload
 crypto/async_tx/async_xor.c: xor and xor zero sum offload