mm-video: revert usage of flag GRALLOC_USAGE_PRIVATE_CP_BUFFER

Obsolete the custom flag added to notify usage of secure buffers. Now all
secure buffers are allocated based on the flag GRALLOC_USAGE_PROTECTED

Change-Id: I92a87f402892d5758fa9adef8ae734d1b8be2c83
Merge "mm-video: revert usage of flag GRALLOC_USAGE_PRIVATE_CP_BUFFER" into cm-10.2