msm: camera2_v2: Return proper v4l2 buffer status for empty frames

Notifying the client about empty buffers through v4l2 events is
rather complicated and prone to timing issues. To avoid the
possibility of having the client use any unprocessed buffers,
set their v4l2 flags accordingly.

Bug: 63176996
Test: Complete Camera CTS
Signed-off-by: Emilian Peev <epeev@google.com>
Change-Id: Ice37d4985167983f0bf2ef97dbd7f4170cd76593
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>