Allow multiple Sensor Flush operations

Flush operations need to be tracked so we get the right number
of flush responses. This CL ensures that each flush response
gets handled.

(This is different from normal sensor events. Each new sensor
event overwrites the previous event, even if the previous event's
values have not been handled.)

Bug: 37465457

Test: This CTS test now passes:
      CtsSensorTestCases
      android.hardware.cts.SensorIntegrationTests#testSensorsMovingRates

CP from oc-emu-dev I6156732990d725bfe79a86c6370b0ff93c44102a

Change-Id: I66cfc0714919b44b1cf7e83af16cc78d3a16147e
1 file changed