Camera: fix RequestBufferStateMachine bug

The old implementation only toggle idle when waitUnitlDrained
is explicitly called, but there are some cases where
application don't need to call waitUntilDrained but can still
expect the device goes into idle.

Test: CTS on Pixel3 equipped with webcam HAL
Bug: 109829698
Change-Id: I48c26abcc9c2f1263c2360611c935fc317745e59