crypto: atmel-aes - improve performances of data transfer

This patch totally reworks data transfer.

1 - DMA

The new code now fully supports scatter-gather lists hence reducing the
number of interrupts in some cases. Also buffer alignments are better
managed to avoid useless copies.

2 - CPU

The new code allows to use PIO accesses even when transferring more than
one AES block, so futher patches could tune the DMA threshold
(ATMEL_AES_DMA_THRESHOLD).
Moreover, CPU transfers now have a chance to be processed synchronously,
hence reducing the latency by avoiding context switches when possible
(less interrupts to process, less scheduling of the 'done' task).
Indeed the 'DATA READY' bit is polled only one time in the Interrupt
Status Register before enabling then waiting for the associated interrupt.
In some condition, this single poll is enough as the data have already
been processed by the AES hardware and so are ready.
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>