mm-video-v4l2: Protect buffer access and increase input buffer size

Protect buffer access for below scenarios:

*Increase the scope of buf_lock in free_buffer to avoid access
 of freed buffer for both input and output buffers. Also, add check
 before output buffer access.

*Disallow allocate buffer mode after client has called use buffer.

Allocate additional 512 bytes of memory for input buffers on top of
allocation size as per hardware requirement

Change-Id: I722ab9b6ecff20dcb97bc3b02830ef484e8bd495
Author: Santhosh Behara <santhoshbehara@codeaurora.org>
Bug: 64340487
Test: PoC before/after
Merged-In: Icc65fe43134493fefe6e420ca818f60995084871
Merged-In: I70fa1dc7ac43b9281209955afc30f6737ce25f0e