video: auo_k190x: add code shared by controller drivers

The AUO-K190X controllers share a very similar set of commands and
can therefore also share most of the driver code.

Signed-off-by: Heiko Stübner <heiko@sntech.de>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>