DO NOT MERGE mm-video-v4l2: vdec: add safety checks for freeing buffers

Allow only up to 64 buffers on input/output port (since the
allocation bitmap is only 64-wide).

Do not allow changing theactual buffer count while still
holding allocation (Client can technically negotiate
buffer count on a free/disabled port)
Add safety checks to free only as many buffers were allocated.

Fixes: Security Vulnerability - Heap Overflow and Possible Local
Privilege Escalation in MediaServer (libOmxVdec problem #3)
Bug: 27532282 27661749

Change-Id: I06dd680d43feaef3efdc87311e8a6703e234b523
