diag: dci: Add additional buffers to process DCI data

DCI clients have only one buffer to store the data and the copy to
user space is synchronous. Have multiple buffers to process incoming
DCI data and copy it to the user space asynchronously. Also generalize
the buffer handling for different DCI processors.

Change-Id: I74db4d49167b4a7e1febd857a5bb49fe77486bb7
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>