MODSIGN: Panic the kernel if FIPS is enabled upon module signing failure

If module signing fails when the kernel is running with FIPS enabled then the
kernel should panic lest the crypto layer be compromised.  Possibly a panic
shouldn't happen on cases like ENOMEM.

Reported-by: Stephan Mueller <stephan.mueller@atsec.com>
Signed-off-by: David Howells <dhowells@redhat.com>