crypto: scomp - Remove support for some non-trivial SG lists

As the only user of acomp/scomp uses a trivial single-page SG
list, remove support for everything else in preprataion for the
addition of virtual address support.

However, keep support for non-trivial source SG lists as that
user is currently jumping through hoops in order to linearise
the source data.

Limit the source SG linearisation buffer to a single page as
that user never goes over that.  The only other potential user
is also unlikely to exceed that (IPComp) and it can easily do
its own linearisation if necessary.

Also keep the destination SG linearisation for IPComp.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>