SEC1 doesn't support scatter/gather, SEC1 doesn't handle link tables.
Therefore, for SEC1 we have to do it by SW. For that, we reserve
space at the end of the extended descriptor, in lieu of the space
reserved for the link tables on SEC2, and we perform sg_copy() when
preparing the descriptors

We also adapt the max buffer size which is only 32k on SEC1 while it
is 64k on SEC2+
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>