rfc3961: Add a kernel rfc3961 implementation

rfc3961: Add a kernel rfc3961 implementation

Add the necessary mechanisms to build Heimdal's libkrb5/crypto_*.c in
the kernel. This provides the kernel module with a RFC3961
implementation.

In theory this could also be used to provide a RFC3961 implementation
on top of an EVP-based crypto library in userspace, but at the moment
we're just using Heimdal directly for this.

Change-Id: Ie57391da0dabd2dca8b305e23f0c0faa056a4675
Reviewed-on: http://gerrit.openafs.org/3948
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>