Support for broadcoms multifunctional devices

bnc#841170, fate#316090

and cleanup and so on.
Ah, I only realized now, when trying to replace `allow` with `expect` (because it is an outgoing message of the tested method, so it should be mocked instead of stubbed):
This stubs `SCR.Read` for *any* path!

Please hold on, I will push my proposed fix.