et: add etss801u driver

This driver handles EgisTec SS801U device, ID 1c7a:0801

Reported-by: Fabian Zaremba <fabian@youremail.eu>
Signed-off-by: Alexey Prokopchuk <alexpro@homelan.lg.ua>
Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>