crypto: caam - replace sec4_sg pointer with array

Since the extended descriptor includes the hardware descriptor, and the
sec4 scatterlist immediately follows this, we can declare it as a array
at the very end of the extended descriptor.  This allows us to get rid
of an initialiser for every site where we allocate an extended
descriptor.

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