Notify HAL when events are read

As defined in the HAL specification, the client of the HAL (framework or
VTS) needs to set the EVENTS_READ flag when it fetches samples out of
the FMQ, to support blocking write mode.

Bug: 135442877
Test: run VTS on a device supporting HAL 2.0
Change-Id: Ic7755e869b999b638086275e4e579a84600be314