xiaomi-platina: new device

This adds basic support for Xiaomi Mi 8 Lite This device is pretty similar to Xiaomi Redmi Note 7 (xiaomi-lavender) which shares the same sdm660 chipset.

For downstream kernel: Works: flashing and booting with fastboot, USB(rndis and OTG), framebuffer, weston, touchscreen, battery charging Doesn't: WiFi, bt, gpu, audio

For mainstream kernel: Using linux-postmarketos-qcom-sdm660 and the dtb for xiaomi-lavender, kernel boots and dmesg can show through uart, 8 CPUs are up, and everything else doesn't work.