HID: roccat: Add support for Isku keyboard

This patch adds support for Roccat Isku keyboard.
Userland tools can 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>