Enable build support for high-bitdepth by default

This causes the HBD operating path to be compiled by default, allowing
default builds to handle all AV1 profiles, instead of only Profile 0.
This doesn't change the current behaviour of the code.

This will help ensuring the HBD operating path continues to compile.

BUG=aomedia:460

Change-Id: I8774b9586b1da479ce3882df482ac3cd3048a9d5
5 files changed