[PATCH] Add missing ifdef for VIA RNG code

Almost all the code for the VIA RNG is guarded with __i386__ #ifdefs,
the only exception being the enumeration of RNG types which is used to
index into the rng_vector ops array.  This patch adds an ifdef around
that for consistency and since the guard makes a difference when adding
new RNG types on non-i386 hardware.

Signed-Off-By: Mark Brown <broonie@sirena.org.uk>
Signed-Off-By: Jeff Garzik <jeff@garzik.org>