some case failed(bitrate range out of 10%) for Vdenc cbr and vbr on SKL/KBL/GLK/APL

[wangzj0601]

System Environment

=======
SW:
libyami 1.2.0
APL/KBL/BSW:libva: commit b65a3d9deacb72bd9f96d3e023d4f8ed58bd8d0a
intel-driver:1.8.4.pre1 (commit ae8831f)
SKL/GLK:libva: commit b65a3d9deacb72bd9f96d3e023d4f8ed58bd8d0a
intel-driver:1.8.4.pre1 (commit 7f50a13)
Libdrm: 2.4.70
xf86-video-intel: 2.99.917
kernel: 4.12.0-rc2 KBL GLK APL BSW / 4.13.0-rc1 SKL
OS: 14.04
HW:
KBL-U
CPU: Dual core; Genuine Intel(R) CPU 0000 @ 2.60GHz
GPU: PCI ID 8086:5916, GT2
Memory: 6G
GLK
CPU: Dual core; Genuine Intel(R) CPU @ 1.10GHz
GPU: PCI ID 8086:3184, GT2
Memory: 4G
Broxton-P
CPU: 4 cores; Genuine Intel
GPU: PCI ID 8086:5a84, APL HD Graphics 505
Memory: 8G
SKL-S
CPU: 4 cores; Intel(R) Core™ i5-6600K CPU @ 3.50GHz
GPU: PCI ID 8086:1912, GT2
Memory: 8G
BSW
CPU: 4 cores; Intel(R) Pentium(R) CPU N3700 @ 1.60GHz
GPU: PCI ID 8086:22b1, GT2
Memory: 4G
Regression?

Bug detailed description

there are some Vdenc CBR and VBR cases whose output bitrate can't meet the criteria for input bitrate((output bitrate - input bitrate)/input bitrate * 100% <= 10%).
Reproduce Steps

take one vbr case for sample on KBL

1. yamitranscode -i /root/media_streams/encoderbitstreams/4K_2013_3840_2160_300frames.yuv -s I420 -W 3840 -H 2160 -b 5000 -c AVC --rcmode VBR --ipperiod ip --lowpower -f 30 -o 4K_2013_3840_2160_300frames.yuv-5000-ip-vbr.h264 --intraperiod 30 --target-percnetage 95 --vbv-buffer-fullness 20480000 --vbv-buffer-size 40960000
2. yamidecode -i ./4K_2013_3840_2160_300frames.yuv-5000-ip-vbr.h264 -m 1 and view the video
3. find that it has garbage during play the video,
4. compare output bitrate calculated by test script with refrence bitrate, find it is out of 10% target.
   failed case:
   SKL/APL:
   CBR:
   MOBILE_352x288_30_orig_01.yuv-150-1-cbr CBR 150 170.76 21.08648 30.47866 30.03692 13.00 FAIL
   4K_2013_3840_2160_300frames.yuv-3000-ip-cbr CBR 3000 8911.68 26.98062 40.92915 41.17392 197.00 FAIL
   4K_2013_3840_2160_300frames.yuv-5000-ip-cbr CBR 5000 9135.57 26.99878 40.97467 41.19167 82.00 FAIL
   4K_2013_3840_2160_300frames.yuv-10000-ip-cbr CBR 10000 11321.99 27.66556 41.23907 41.48223 13.00 FAIL
   VBR:
   4K_2013_3840_2160_300frames.yuv-3000-ip-vbr VBR 3000 9739.82 27.00438 41.05275 41.28552 224.00 FAIL
   4K_2013_3840_2160_300frames.yuv-5000-ip-vbr VBR 5000 10593.33 27.04720 41.15118 41.38706 111.00 FAIL
   4K_2013_3840_2160_300frames.yuv-10000-ip-vbr VBR 10000 14323.20 27.73767 41.40867 41.67013 43.00 FAIL
   GLK/KBL
   CBR:
   4K_2013_3840_2160_300frames.yuv-3000-ip-cbr CBR 3000 8911.68 26.98062 40.92915 41.17392 197.00 FAIL
   4K_2013_3840_2160_300frames.yuv-5000-ip-cbr CBR 5000 9135.57 26.99878 40.97467 41.19167 82.00 FAIL
   4K_2013_3840_2160_300frames.yuv-10000-ip-cbr CBR 10000 11321.99 27.66556 41.23907 41.48223 13.00 FAIL
   VBR:
   4K_2013_3840_2160_300frames.yuv-3000-ip-vbr VBR 3000 9739.82 27.00438 41.05275 41.28552 224.00 FAIL
   4K_2013_3840_2160_300frames.yuv-5000-ip-vbr VBR 5000 10593.33 27.04720 41.15118 41.38706 111.00 FAIL
   4K_2013_3840_2160_300frames.yuv-10000-ip-vbr VBR 10000 14323.20 27.73767 41.40867 41.67013 43.00 FAIL
   Expected Result
   =============
   For all test cases, should be (output bitrate - input bitrate)/input bitrate * 100% <= 10%
   Actual Result
   ===========
   6 cases failed on KBL/GLK, 7 cased failed on APL/SKL