crypto: octeontx2 - get engine group number for asymmetric engine

crypto: octeontx2 - get engine group number for asymmetric engine

Cryptographic Accelerator Unit (CPT) support different engine groups, one
for asymmetric algorithms (only AE engines in this group), one for the
most common symmetric algorithms (all SE and all IE engines in this group),
and one for other symmetric algorithms (only SE engines in this group).

For symmetric engine (SE), we obtain the group number using
"MBOX_MSG_GET_ENG_GRP_NUM" mailbox. Let's follow a similar approach to
determine the group number for asymmetric engine (AE).

Signed-off-by: Amit Singh Tomar <amitsinght@marvell.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>