xiaomi-polaris: new device

Add support for the Xiaomi Mi Mix2s

Currently working features:

• Wi-Fi, GPU, Venus, Haptics, Battery FG, Touchscreen, Bluetooth
• Modem (message and lte data work, calls can be made but no sound in and out), Audio (Speakers work fine, type-c headphone doesn't work yet). Tried to add q6voiced.conf, but it doesn't solve the calling sound issue. Have no idea how to fix it.

Make it Draft as this MR in sdm845-mainline haven't be merged yet.