mm-video-v4l2: venc: Use client allocated memory if available

IL client may free the buffer and calls for free buffer on IL
component to free the buffer header. It may happen that the IL
component may reject the free buffer due to various reasons.
In such scenario, client might have already freed the memory
allocated by client (such scenario will appear in use buffer
mode of buffer allocation). Now accessing client buffer in
such scenario may lead to use after free vulnerability.
Added a flag to indicate if the client buffer is available to
perform any operation on the client allocated memory. If not,
restrict from doing any operation on client memory.

Bug: 62452543
CRs-Fixed: 2106434
Test: build & boot
Test: cts-tradefed run cts-dev --module CtsMediaTestCases --compatibility:module-arg
CtsMediaTestCases:include-annotation:android.platform.test.annotations.RequiresDevice

Change-Id: If24c36b9a1cca36a2728d3aec8ab589a48a9da35
Author: Vikash Garodia<vgarodia@codeaurora.org>