STOPSHIP: Roll forward: Add UidCpuPower global setting

This will help us run P/H experiments by controlling the
uid cpu power system property through P/H.

b/70517018
Test: adb shell settings put global sys_uidcpupower 1
      verify via getprop sys.uidcpupower

Change-Id: I8cf7365be885ef4910e37d3f993ba3079e15a37d