crypto: caam - unregister algorithm only if the registration succeeded

To know if a registration succeeded added a new struct,
caam_akcipher_alg, that keeps, also, the registration status.
This status is updated in caam_pkc_init and verified in
caam_pkc_exit to unregister an algorithm.

Fixes: 1b46c90c ("crypto: caam - convert top level drivers to libraries")
Signed-off-by: Iuliana Prodan <iuliana.prodan@nxp.com>
Reviewed-by: Horia Geanta <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>