Ignore touches outside of Udfps Overlay bounds

Udfps overlay is fullscreen so unnecessary ellipse checks can be removed
by only checking touches that are within the overlay bounds (bottom half
of screen). These touches are likely way off from the sensor.

Bug: 274162395
Test: atest SystemUITests:com.android.systemui.biometrics
Change-Id: I56af14d9817b5b4719a20d40dcc69f961003b1be