Add flag to control motion prediction

This flag will be used as a global override for system predictions.
Even if a device specifies that it supports predictions, this flag can
be used to disable them.

Bug: 210158587
Test: adb shell setprop persist.input.enable_motion_prediction true
Test: tested with MotionPrediction app
Change-Id: If901387aa01ac8704d8ee22c26978a16577ee0aa