mm-video-v4l2: Protect buffer lifecycle with lock

IL Client may choose to free the buffer which might
be in-use by IL component. This may lead to use-after
free situation.
Protect buffer lifecycle with a lock to ensure that
IL component operates on a buffer which exists.

Fixes bug 62452543
 Security Vulnerability - Heap use after free in libOmxVenc

CRs-Fixed: 2062772
Test: build & boot
Test: cts-tradefed run cts-dev --module CtsMediaTestCases --compatibility:module-arg
CtsMediaTestCases:include-annotation:android.platform.test.annotations.RequiresDevice

Author: Vikash Garodia <vgarodia@codeaurora.org>

Change-Id: I0fdb4051c94044e032c257febbe2ba1c7e4d6c7e