Validate display size on init

[nyaray]

At some point, we should port the screen size checking from the python inky library so that we can fail fast if we detect that the wrong device has been specified in our init opts.

[nyaray]

Since LUTs are about voltage control we should probably implement the eeprom-based display-size validation as there might otherwise be a risk that we basically allow users to tell the screen to fry itself internally... in the worst case.