anv: stub internal android code

anv: stub internal android code

This reduces the amount of #ifdef ANDROID we'll have to have inside
the driver. Potentially offering better coverage of the android
extensions.

v2: Move anv_android.h include before anv_entrypoints.h (Tapani)
    Fix autotools android build (Lionel)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>