- disable vsx on ppc64le to fix build failure

- update to version 1.8.0
This release focused on encoding performance for realtime and VOD use cases.
- Upgrading:
This adds and improves several vp9 controls. Most are related to SVC:
VP9E_SET_SVC_FRAME_DROP_LAYER:
- Frame dropping in SVC.
VP9E_SET_SVC_INTER_LAYER_PRED:
- Inter-layer prediction in SVC.
VP9E_SET_SVC_GF_TEMPORAL_REF:
- Enable long term temporal reference in SVC.
VP9E_SET_SVC_REF_FRAME_CONFIG/VP9E_GET_SVC_REF_FRAME_CONFIG:
- Extend and improve this control for better flexibility in setting SVC
pattern dynamically.
VP9E_SET_POSTENCODE_DROP:
- Allow for post-encode frame dropping (applies to non-SVC too).
VP9E_SET_SVC_SPATIAL_LAYER_SYNC:
- Enable spatial layer sync frames.
VP9E_SET_SVC_LAYER_ID:
- Extend api to specify temporal id for each spatial layers.
VP9E_SET_ROI_MAP:
- Extend Region of Interest functionality to VP9.
- Enhancements:
2 pass vp9 encoding has improved substantially. When using --auto-alt-ref=6,
we see approximately 8% for VBR and 10% for CQ. When using --auto-alt-ref=1,
the gains are approximately 4% for VBR and 5% for CQ.
For real-time encoding, speed 7 has improved by ~5-10%. Encodes targeted at
screen sharing have improved when the content changes significantly (slide
sharing) or scrolls. There is a new speed 9 setting for mobile devices which