samsung-gt510wifi: new device (Samsung Galaxy Tab A 9.7 Wifi (2015) (SM-T550))

This PR adds mainline device packages for:

Samsung Galaxy Tab A 9.7 Wifi (2015) - SM-T550 (gt510wifi)

(Whatever I'm) Working (on):

• Booting
• USB Gadget Mode
• WiFi
• Bluetooth
• Display (Working on it)
• Brightness (See Display)
• GPU (Freedreno, see Display)
• Touchscreen

Current port is based on work by the MSM8916-Mainline project, it depends on lk2nd and their kernel fork. Device package is based on a5ulte.