SUNRPC: Add Kconfig dependency on CRYPTO_KRB5

SUNRPC: Add Kconfig dependency on CRYPTO_KRB5

The rpcsec_gss_krb5 module currently contains its own Kerberos 5
crypto implementation (key derivation, encryption, checksumming)
that duplicates functionality available in the common crypto/krb5
library. As a first step toward migrating to that library, add a
Kconfig select so that building rpcsec_gss_krb5 pulls in the
common Kerberos 5 crypto support.

The per-enctype Kconfig options (AES_SHA1, CAMELLIA, AES_SHA2)
remain: they continue to gate which encryption types are offered
by the GSS mechanism. The individual crypto algorithm selects
they carry become redundant once the migration is complete, since
CRYPTO_KRB5 already selects all needed ciphers and hashes.

Assisted-by: Claude:claude-opus-4-6
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Anna Schumaker <anna.schumaker@hammerspace.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>