xiaomi-laurel: new device (Xiaomi Mi A3)

A quirky device, the last Mi Ax phone in the line. - Powered by
Snapdragon 665 (SM6125, codenamed Trinket), 8 cores, 4 clocked a 2.0
GHz and 4 more clocked at 1.8 GHz. 4-6 GB of RAM, 64-128 GB of UFS
storage, 720p 6.09" AMOLED display, a 48 Mpx quad-bayer camera (plus two
more on the back and one on the front) and an under display fingerprint
sensor which may be impossible to ever implement... *sigh*

Mainline kernel as of now is pretty minimal (framebuffer display, USB
networking). No UFS support (yet!).