device-samsung-klte: add kltechn variant

This MR tries to add a variant of klte, kltechn (SM-G900[689][VW]), which has a slightly different I2C GPIO arrangement.

It's currently a draft because I need to wait for Rong to send out the kltechn patch to mainline.

GPU is added in addition, just because it's already there for hlte and this enables me to test with mobile-friendly UIs.