[AF_RXRPC/AFS]: Arch-specific fixes.

Fixes for various arch compilation problems:

 (*) Missing module exports.

 (*) Variable name collision when rxkad and af_rxrpc both built in
     (rxrpc_debug).

 (*) Large constant representation problem (AFS_UUID_TO_UNIX_TIME).

 (*) Configuration dependencies.

 (*) printk() format warnings.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>