etnaviv: store connection from dev to pipe

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
etnaviv: we need at least a chip model != 0

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
etnaviv: add very very basic ringbuffer impl

etna_ringbuffer_flush() is a stub!

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