random32: mix in entropy from core to late initcall

      Currently, we have a 3-stage seeding process in prandom():

Phase 1 is from the early actual initialization of prandom()
subsystem which happens during core_initcall() and remains
most likely until the beginning of late_initcall() phase.
Here, the system might not have enough entropy available
for seeding with strong randomness from the random driver.
That means, we currently have a 32bit weak LCG() seeding
the PRNG status register 1 and mixing that successively
into the other 3 registers just to get it up and running.

Phase 2 starts with late_initcall() phase resp. when the
random driver has initialized its non-blocking pool with
enough entropy. At that time, we throw away *all* inner
state from its 4 registers and do a full reseed with strong
randomness.

Phase 3 starts right after that and does a periodic reseed
with random slack of status register 1 by a strong random
source again.

A problem in phase 1 is that during bootup data