genesys: Add basic support for CanoScan 8600F
This PR adds support for CanoScan 8600F. Regular and transparency scans work up to 1200 dpi. Higher resolutions are currently not yet supported.
The inclusion of transparency support is an important milestone, because this is the first scanner in genesys backend where it is actually enabled.
The PR includes several changes that are unrelated to 8600F, yet change the behavior of all scanners under GL843 backend.