Merge changes from topics "master-I2a659a980d32912bec5a1c0869c88e06a29cf9ce", "master-I6852683ad14a8fa6b0fc22f39e0c9c7823d1da2c", "master-I8f8b467a4dfad68f6e2e53954b5944c6155de782", "master-I9ef8e57207aa96ec1f8193e8d8cd5dfc47567d38", "master-Id17d162d142a2595e54e163f5faaf7dcf9b68e35"

* changes:
  Add a sm8450_mini target.
  Create a mini configuration for the dragonboards.
  Factor out the full device configuration.
  Move the architecture definitions into the device-specific BoardConfigs.
  Remove pixel3_mainline target.