avcodec/v410dec: add support for frame and slice threading

avcodec/v410dec: 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 v410 input data for testing:
 ./ffmpeg -y -i 4k_422.ts  -c:v v410 -vframes 10 test.avi

master:
./ffmpeg -y -stream_loop 1000 -i ./test.avi -benchmark -f null -
frame=10010 fps= 37 q=-0.0 Lsize=N/A time=00:38:26.30 bitrate=N/A speed= 8.6x
video:5240kB audio:432432kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
bench: utime=166.016s stime=102.192s rtime=268.120s
bench: maxrss=273400kB

patch applied:
./ffmpeg -y -threads 2 -thread_type slice -stream_loop 1000 -i ./test.avi -benchmark -f null -
frame=10010 fps= 53 q=-0.0 Lsize=N/A time=00:38:26.30 bitrate=N/A speed=12.3x
video:5240kB audio:432432kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
bench: utime=165.135s stime=100.456s rtime=187.994s
bench: maxrss=275476kB

./ffmpeg -y -threads 2 -thread_type frame -stream_loop 1000 -i ./test.avi -benchmark -f null -
frame=10010 fps= 61 q=-0.0 Lsize=N/A time=00:38:26.30 bitrate=N/A speed=14.1x
video:5240kB audio:432432kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
bench: utime=171.386s stime=122.102s rtime=163.637s
bench: maxrss=340308kB

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