lecroy-xstream: Use best-effort strategy for unknown models

lecroy-xstream: Use best-effort strategy for unknown models

As there is a huge range of supported LeCroy scopes, naming
the IDN response for every single one of them is going to be
impossible. Hence, it makes more sense to treat all LeCroy
devices as if they were scopes and supported. This approach
lets users try to see how far they get and if they run into
issues, they can then be treated separately - e.g. by creating
a custom device profile.
Unless we do this, the vast majority of LeCroy scopes will
not be recognized by the driver.