libvpx: Pull from upstream

Upstream hash: d4a47a6cc0d869bea3071c15bc61da6836026d0b

Pull latest libvpx from upstream. This fixes a few vp9 encoder bugs and
includes some optimizations. Also fixes a couple of configure flags in
x86 to be consistent with the rest.

Change-Id: Ic58e0b03cce832571a35ec73eec559cdf881d1f5
Merge "libvpx: Pull from upstream"
libvpx: disable accidentally enabled neon code

upstream's configure behavior changed and an extra flag needed to
be passed to disable all the neon code for target armv7a.

Change-Id: I773fdf29bdd678aa56cd7cf5d0942cd3f456de73
Merge "libvpx: disable accidentally enabled neon code"