Export fortuna PRNG to the kernel where needed

Some systems do not supply a useful implementation of osi_readRandom()
but we want to use real random numbers in the kernel for setting the
RX epoch and connection ID.

Build hcrypto's fortuna PRNG into the rand-kernel interface we expose,
and export RAND_seed so that we can pass in entropy from userland.

If we are going to use the fortuna implementation, we must include the
fortuna implementation in the objects linked into the kernel module; do
this only on the architectures where it is needed.

Change-Id: I614d2bd9ac52803ec3b9572cc694cd836c8427dd
Pass entropy into the kernel at afsd startup

Used to seed our in-kernel fortuna PRNG, if we are using fortuna
instead of a kernel-provided PRNG.
We can pass 160 bytes directly in the syscall arguments; that should
be enough.

Change-Id: Iea2fef0b333e68f2dd61bfa809e8bff9f5b7ffd5
Hack kernel fortuna on always

To actually test that the in-kernel fortuna has a chance of linking
and running.

Change-Id: I59e3b60e00249c5958deafb58e3a593aacb2fd3c