crypto: marvell/cesa - factor out adding an operation and launching it

Add a helper to add the fragment operation block followed by the DMA
entry to launch the operation.

Although at the moment this pattern only strictly appears at one site,
two other sites can be factored as well by slightly changing the order
in which the DMA operations are performed.  This should be harmless as
the only thing which matters is to have all the data loaded into SRAM
prior to launching the operation.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>