crypto: gcm - fix incompatibility between "gcm" and "gcm_base"

GCM instances can be created by either the "gcm" template, which only
allows choosing the block cipher, e.g. "gcm(aes)"; or by "gcm_base",
which allows choosing the ctr and ghash implementations, e.g.
"gcm_base(ctr(aes-generic),ghash-generic)".

However, a "gcm_base" instance prevents a "gcm" instance from being
registered using the same implementations.  Nor will the instance be
found by lookups of "gcm".  This can be used as a denial of service.
Moreover, "gcm_base" instances are never tested by the crypto
self-tests, even if there are compatible "gcm" tests.

The root cause of these problems is that instances of the two templates
use different cra_names.  Therefore, fix these problems by making
"gcm_base" instances set the same cra_name as "gcm" instances, e.g.
"gcm(aes)" instead of "gcm_base(ctr(aes-generic),ghash-generic)".

This requires extracting the block cipher name from the name of the ctr
algorithm.  It also requires starting to verify that the algorithms are
really ctr and ghash, not something else entirely.  But it would be
bizarre if anyone were actually using non-gcm-compatible algorithms with
gcm_base, so this shouldn't break anyone in practice.

Fixes: d00aa19b ("[CRYPTO] gcm: Allow block cipher parameter")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>