crypto: ccp - Register SNP panic notifier only if SNP is enabled

Currently, the SNP panic notifier is registered on module initialization
regardless of whether SNP is being enabled or initialized.

Instead, register the SNP panic notifier only when SNP is actually
initialized and unregister the notifier when SNP is shutdown.

Reviewed-by: Dionna Glaze <dionnaglaze@google.com>
Reviewed-by: Alexey Kardashevskiy <aik@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>