provide operating performance point info about each cpu via kstats.

provide operating performance point info about each cpu via kstats.

if there's a device tree and it provides information about cpu
speed, expose those stats. this is particularly useful on big.little
or systems with multiple clusters/clock domains or cores that can
scale indepenently because it can report the actual speed each cpu
is operating at independently.

ok patrick@ who used an earlier version of this diff to work on cpu
scaling on an rk3588 system.