Adjust initialization of random(9) so it is usable earlier.

Adjust initialization of random(9) so it is usable earlier.

A few existing SYSINITs expect the in-kernel PRNG (random(9)) to be
useable at SI_SUB_RANDOM / SI_ORDER_ANY.  However, the random(4) overhaul
merged for 10.0 performs all of its initialization at SI_SUB_DRIVERS
(since it is tied in with creating the /dev/random character device).

This has changed in HEAD where the random initialization is split such
that the in-kernel random(9) is initialized at SI_SUB_RANDOM and the
supporting bits for userland random(4) (such as /dev/random) are initialized
later.

However, the changes in HEAD are large and invasive.  Instead, this change
is being directly committed to stable/10.

This change moves most of the random(9)/random(4) initialization to
SI_SUB_RANDOM with the exception that the creation of the harvesting kernel
process and the /dev/random character device are deferred to new
SYSINITs that run at SI_SUB_DRIVERS.

This fixes the "random device not loaded; using insecure entropy" message
output during boot on some systems.

PR:		205800
Reviewed by:	markm, so@
Approved by:	so
Approved by:	re (gjb)
Tested by:	Mark Saad <nonesuch@longcount.org>

git-svn-id: svn://svn.freebsd.org/base/stable/10@295480 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f