C2BqBuffer: resolve 3 way deadlock

Do not hold lock when IPC call is expected from HAL.

C2SurfaceSyncObj is shared lock between framework and HAL. HAL process
can have only one thread to handle IPC from HAL to framework.
Therefore Holding C2SurfaceSyncObj from HAL during IPC call could
trigger deadlock. The exact scenario is as follows.

Thread #1:(HAL -> framework IPC) HIDL call onInputBuffersReleased()
            calls to feedInputBufferIfAvailable(). Since this is using
            HAL IPC thread, this will block Thread #3. This is waiting
            for mOuput mutex which is held by Thread #2.
Thread #2:(framework) discardBuffer() holds mOutput mutex which blocks
            Thread #1. But this is waiting for C2SurfaceSyncObj which is
            held by Thread #3.
Thread #3:(HAL) Dtor of C2BufferQueueBlockPoolData is holding
            C2SurfaceSyncObj, therefore this will block #2. This thread
            is waiting for HIDL IPC thread to be free in order for
            'igbp->cancel()', but HIDL IPC thread is already occupied by
            Thread #1.

Bug: 246707566
Test: atest android.media.decoder.cts.AdaptivePlaybackTest
Test: atest android.media.decoder.cts.DecoderTest
Change-Id: I6a9540d3b4d03806cd40bb4f89a234a6b77758a9