fifo: handle overrun correctly

On overrun, allow a non-throttling reader to read any frames not yet overwritten.

Also provide an exact count of lost frames rather than an estimate,
when the fifo is configured with a non-power-of-2 capacity.

Bug: 36003483
Test: media.log and fifo interactive unit test
Change-Id: Ia0a7b6f1043f1cd34f6b4fa779785afeff34c5c9
1 file changed