[Vp8_decode]one case will occurs gpu hang when do vp8 decode on CFL

[wangzj0601]

Test enc
Platform: CFL
Kernel version: 4.14.0-rc1
libva: 2.0.1.pre1 ce1960eec8d94d0badb7ede2f80c5dd4829640e2
intel_driver: 2.0.1.pre1 49976650aeac44f7fc638dc6496867b1bafa43d1
libva-utils: 2.0.1.pre1 071dd74acbf6ddf675924dc579771e226f87f7a9
libyami: a1f863c
libyami-utils: 8cfdf784719be0499b9839a6a94d277856c4ac94

Reproduce steps

1. run command dmesg |grep hang, make sure no gpu hang info
2. yamidecode -i 4K_HOBIT3_3840x2160_1000frames.yuv_cqp_qp120_ip.vp8 -m -1 -f I420
3. run command dmesg |grep hang, find gpu hang occurs

Expected result
no gpu hang when decode this stream

Actual result
gpu hang occurs when do this stream on CFL with Ubuntu 16.04 and kernel 4.14.0-rc1.
this issue can not be duplicated on KBL with Ubuntu 16.04 and kernel 4.10.0-20-generic.
this issue can be duplicated on KBL with Ubuntu 14.04 and kernel 4.14.0-rc1.

[xuguangxin]

@wangzj0601 , is this a driver issue?