HID: roccat: Add support for Roccat Arvo keyboard

This patch add support for Roccat Arvo keyboard. Arvo has 5 additional
configurable buttons and the ability to deactivate certain keys.
Userland tools can soon be found at http://sourceforge.net/projects/roccat



Signed-off-by: Stefan Achatz <erazor_de@users.sourceforge.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>