add stub vivante_hw_init(..)

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
add missing return

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
add a general vivante_gpu_init(..) function

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>