Default accel Z direction value to +9.8

Default the accelerometer defaut Z value to +9.8 to indicate a
more 'natural' resting position of flat with screen up for the
device.

Bug: 242736284
Test: Presubmits, vts VtsHalSensorsV2_0TargetTest.
Change-Id: I92357119173dbc99a0a6665de5d733286ac30c3e