Let the system process set the saturation boost

The display manager service will need to call this code early
in the boot process, but before the hardware test calling permission
check can pass (it depends on the order of initalization of other
services like sensors).

Bug: 62238038
Test: Manual (modified display manager service)
Change-Id: I46a673ba971e566a0b9e023005c41fa54603cd1f