Add support for UC-Logic Wireless Tablet TWHL850.
It is known to be sold as Genius MousePen M508W.

This tablet has a bug in the default (compatibility) mode which is used in this
driver: frame button assignments are mixed up. This is to be fixed with a driver
supporting the vendor-specific protocol.
Signed-off-by: Nikolai Kondrashov <spbnick@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>