DO NOT MERGE mm-video-v4l2: vdec: Avoid processing ETBs/FTBs in invalid states

(per the spec) ETB/FTB should not be handled in states other than
Executing, Paused and Idle. This avoids accessing invalid buffers.
Also add a lock to protect the private-buffers from being deleted
while accessing from another thread.

Bug: 27890802
Security Vulnerability - Heap Use-After-Free and Possible LPE in
MediaServer (libOmxVdec problem #6)

CRs-Fixed: 1008882

Change-Id: Iaac2e383cd53cf9cf8042c9ed93ddc76dba3907e

omx_vdec::ts_arr_list::ts_arr_list()
{
    memset(m_ts_arr_list, 0, ( sizeof(ts_entry) * MAX_NUM_INPUT_OUTPUT_BUFFERS) );
}

omx_vdec::ts_arr_list::ts_arr_list()
{
    memset(m_ts_arr_list, 0, ( sizeof(ts_entry) * MAX_NUM_INPUT_OUTPUT_BUFFERS) );
}
