This patch main goal is to improve driver performance by moving the
crypto request from a list to a RDR ring shadow.

This is possible since there is one producer and one consume for this
RDR request shadow and one ring descriptor is left unused.
Doing this change eliminates the use of spinlock when accessing the
descriptor ring and the need to dynamicaly allocate memory per crypto
request.

The crypto request is placed in the first RDR shadow descriptor only
if there are enough descriptors, when the result handler is invoked,
it fetches the first result descriptor from RDR shadow.
Signed-off-by: NOfer Heifetz <oferh@marvell.com>
Signed-off-by: NAntoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>