crypto: omap-sham - DMA initialization fixes for off mode

DMA parameters for constant data were initialized during driver probe().
It seems that those settings sometimes are lost when devices goes to off mode.
This patch makes DMA initialization just before use.
It solves off mode problems.

Fixes: NB#202786 - Aegis & SHA1 block off mode changes

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