motorola-ali: use mainline kernel and add firmware
This will:
- Remove the Moto G6's downstream kernel (was 32-bit, based on Linux 3.18)
- Update the device package to be 64-bit, and use the msm8953-mainline kernel
- Add the optional proprietary firmware blobs
I've tested this using the Gnome-mobile and Plasma-mobile DEs. Display, touch, and graphics are all working well. Wifi is working too, though I didn't test Bluetooth. Audio, battery data, modem, and camera are all currently not working.