crypto: omap-sham - zero-copy scatterlist handling

If scatterlist have more than one entry, current driver uses
aligned buffer to copy data to to accelerator to tackle possible
issues with DMA and SHA buffer alignment.

This commit adds more intelligence to verify SG alignment and
possibility to use DMA directly on the data without using copy
buffer.

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>