avcodec/v210dec: add support for frame and slice threading

avcodec/v210dec: add support for frame and slice threading

1, Test server configure:
[root@localhost ~]# cat /proc/cpuinfo  |grep "model name"
 model name      : Intel(R) Xeon(R) CPU E5-2650 v2 @ 2.60GHz
 model name      : Intel(R) Xeon(R) CPU E5-2650 v2 @ 2.60GHz
 ...

[root@localhost ~]# free -h
              total        used        free      shared  buff/cache   available
              Mem:           102G        1.1G        100G         16M        657M        100G
              Swap:          4.0G          0B        4.0G

2, Test result:
encode the v210 input data for testing:
./ffmpeg -y -i 4k_422.ts  -c:v v210 -vframes 10 test.avi

master:
./ffmpeg -y -threads 1 -stream_loop 1000 -i ./test.avi -benchmark -f null -
frame=10010 fps= 60 q=-0.0 Lsize=N/A time=00:38:26.30 bitrate=N/A speed=13.7x
video:5240kB audio:432432kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
bench: utime=101.869s stime=66.181s rtime=167.996s
bench: maxrss=186552kB

patch applied:
./ffmpeg -y -threads 2 -thread_type slice -stream_loop 1000 -i ./test.avi -benchmark -f null -
frame=10010 fps= 72 q=-0.0 Lsize=N/A time=00:38:26.30 bitrate=N/A speed=16.5x
video:5240kB audio:432432kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
bench: utime=103.562s stime=74.858s rtime=139.599s
bench: maxrss=188616kB

./ffmpeg -y -threads 2 -thread_type frame -stream_loop 1000 -i ./test.avi -benchmark -f null -
frame=10010 fps= 85 q=-0.0 Lsize=N/A time=00:38:26.30 bitrate=N/A speed=19.6x
video:5240kB audio:432432kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
bench: utime=114.310s stime=92.685s rtime=117.693s
bench: maxrss=231896kB

Signed-off-by: Limin Wang <lance.lmwang@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>