hid: egalax: Add support for Wetab

The Wetab tablet dual-touch controller works the same way as the one
in the Joojoo tablet. This patch adds the Wetab to the list of
supported devices, and grabs it accordingly in hid-core.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Cc: Stephane Chatty <chatty@enac.fr>
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>