Fix Venus 8 GPS binary message processing

[IanOsgood]

Old Venus 6 structures (for message A8) had elements that were all two times too large, so it was obviously untested. Write code to split and verify GPS binary packets. Message tags are of form V8xx, where xx is the Venus hex packet ID.

Fix psas_packet and telemetry viewer to match.

[jameysharp]

I think you got this all pretty well done, Ian, so I'm closing this issue. We'll do final testing tomorrow just to be sure.