s390/crypto: simplify init / exit functions

The aes and the des module register multiple crypto algorithms
dependent on the availability of specific CPACF instructions.
To simplify the deregistration with crypto_unregister_alg add
an array with pointers to the successfully registered algorithms
and use it for the error handling in the init function and in
the module exit function.

Reviewed-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>