libcameraservice: allow skipping of autofocus callbacks

Set BOARD_LIBCAMERA_MISSING_AUTOFOCUS to skip autofocus callbacks.
This is needed for Huawei's proprietary libcamera libraries that are
based on Eclair, used by the Huawei U8120, U8150, U8160 and
possibly others.

Change-Id: Ibc5eeda5d01b9db62d9b3c548840be7dee61096d