Systems containing the Cavium HW RNG may have one device per NUMA
node.  A typical configuration is a 2-node NUMA system, which results
in 2 RNG devices.  The hwrng subsystem refuses (and rightly so) to
register more than one device with he same name, so we get failure
messages on these systems.

Make the hwrng name unique by including the underlying device name.
Also remove spaces from the name to make it possible to switch devices
via the sysfs knobs.
Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>