libaom-1.0.0-bp151.2.1

- Enable CONFIG_LOWBITDEPTH. Makes 8-bit decoding faster. The only
  reason this confusingly-named option is not enabled by default
  is that its behavior might not match the 16-bit reference code
  path, and that hardware vendors want to be able to validate
  their designs against it. No actual mismatches have been found.
  See https://bugs.chromium.org/p/aomedia/issues/detail?id=2062

- Pass conditional AOM_TARGET_CPU to cmake, fix build for arm and
  ppc, as well as optimize target cpu for other arches.

- Init, v1.0.0