asix-sigma: concentrate more sample memory interpretation params

asix-sigma: concentrate more sample memory interpretation params

Start moving parameters into the device context which are related to the
interpretation of sample memory content. This can simplify error paths,
allow to release resources late. And ideally sample memory download and
interpretation could spread across several receive callbacks, improving
UI responsiveness. Also makes total and current dimensions available to
deeper nesting levels in the interpretation, which currently don't have
access to these details.