Celeron J3160 with enabled Turbo mode stays at 480MHz (lowest setting) forever and can not lower frequency without Tuebo mode

[Lev Serebryakov]

Hello FreeBSD,

I'm installing latest 12-ALPHA4 on new MiniPC with Celeron J3160 CPU. It
is 1.6GHz CPU with Turbo up to 2.somethingGHz.

If I enable Turbo mode, after booting to FreeBSD it locks at 480MHz
according to dev.cpu.0.freq, and simple "openssl" test confirms it.

If I disable Turbo mode, after booting to FreeBSD it locks at 1600MHz even
if powerd is running.

It looks like some bug in interaction between cpufreq and Turbo mode of
this CPU.