HID: roccat: rename roccat_common functions to roccat_common2

Did this to illustrate my understanding of the firmware generations:
Valo and Kone were 1st generation
Arvo was externaly developed and lies in the middle
All others until now are considered 2nd generation

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