kern/49454: cprng_fast is not available during first pass of device autoconf

[jmcneill%invisible.ca@localhost]

>Number:         49454
>Category:       kern
>Synopsis:       cprng_fast is not available during first pass of device autoconf
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Dec 07 02:20:00 +0000 2014
>Originator:     Jared McNeill
>Release:        7.99.2
>Organization:
Jared McNeill
>Environment:
NetBSD 7.99.2 (ALLWINNER_A80) #140: Sat Dec  6 22:07:43 AST 2014
>Description:
I get the following panic trying to call cprng_fast32 in a driver attach function, when the driver attached at boot time:

panic: kernel diagnostic assertion "off < percpu_nextoff" failed: file "/Users/jmcneill/branches/HEAD/src/sys/kern/subr_percpu.c", line 76 

Seems cprng_fast isn't initialized until after configure in init_main.
>How-To-Repeat:

>Fix: