CPU time min threshold for CpuTimePerUidFreq

Introduce a threshold to exclude small CPU time values in
CpuTimePerUidFreq. They come from more precise accounting in a BPF
program.

The threshold is 10 ms to match the behavior of the time_in_state BPF
predecessor. The reducation in data size is expected be at least 20%.

Bug: 157535126
Test: adb shell cmd stats pull-source 10010
Change-Id: Ia7f2a2ad71831387cffdd6db30da4ce501219d0e