msm: camera2: cpp: Enhance timeout handler for multi-frame processing

The CPP driver can schedule multiple frames to achieve higher
performance. This results in multiple frames to be in pending state
in the driver. When timeout handler is invoked, the condition
of NACK and user event callbacks need to be sequeunced properly.
This change helps to serialize in such a way that the timeout
handler is allowed to complete the frame notification before any
user event callback is handled.

Change-Id: Ie883b1823000085094e39f4c0ae7e10a3d377d16
Signed-off-by: Rajakumar Govindaram <rajakuma@codeaurora.org>