libvpx: Roll latest libvpx

Pulling changes related to fixing a rare bitstream issue on video upscaling.
Also enables VP9 encoder. This is exactly the same as the roll that is
already in master.

Upstream Hash: 8e9c9f118cda45013f14cce7961dcc8df78ffebf

Change-Id: Iba9bb1c1804462014deab20fa6f4c5e4c55a778e
837 files changed