sched_ule(4): Pre-seed sched_random().

I don't think it changes anything, but why not.

While there, make cpu_search_highest() use all 8 lower load bits for
noise, since it does not use cs_prefer and the code is not shared
with cpu_search_lowest() any more.

MFC after: 1 month

(cherry picked from commit ca34553b6f631ec4ec5ae9f3825e3196e172c35d)