crypto: marvell - Add a macro constant for the size of the crypto queue

Adding a macro constant to be used for the size of the crypto queue,
instead of using a numeric value directly. It will be easier to
maintain in case we add more than one crypto queue of the same size.

Signed-off-by: Romain Perier <romain.perier@free-electrons.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>