crypto/nx: Make enable code generic to add new GZIP compression type

Make setup and enable code generic to support new GZIP compression type.
Changed nx842 reference to nx and moved some code to new functions.
Functionality is not changed except sparse warning fix - setting NULL
instead of 0 for per_cpu send window in nx_delete_coprocs().

Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1587114569.2275.1126.camel@hbabu-laptop