Fix encode_app poll error and encode time too long

[longyiluo]

PR描述:

poll error happened when heavy loading.
After isolcpus=1, 2 channels 1080p rtsp happens encode time too long.

详细描述:

root cause:

1. encode_app doesn't QBUF when buffer overflow
2. After isolcpus=1, userspace app needs to balance threads by itself.
   counter measure:
3. queue all v4l2 buffers after buffer overflow
4. dispatch rtsp thread to core 1

关联issue:

fix #347