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.

device/testing/device-xiaomi-polaris/APKBUILD

+# Maintainer: Molly Sophia <mollysophia379@gmail.com>
+
+# Reference: <https://postmarketos.org/devicepkg>
+pkgname=device-xiaomi-polaris
+pkgdesc="Xiaomi Mi Mix 2S"
+pkgver=0.1
+pkgrel=0
+url="https://postmarketos.org"
+license="MIT"
+arch="aarch64"
+options="!check !archcheck"
+depends="
+	linux-postmarketos-qcom-sdm845
+	mkbootimg
+	postmarketos-base
+	postmarketos-update-kernel
+	soc-qcom-sdm845
+	soc-qcom-sdm845-ucm
+"
+makedepends="devicepkg-dev"
+source="
+	deviceinfo
+	phoc.ini
+"
+subpackages="
+	$pkgname-nonfree-firmware:nonfree_firmware
+	$pkgname-phosh
+"
+
+build() {
+	devicepkg_build $startdir $pkgname
+}
+
+package() {
+	devicepkg_package $startdir $pkgname
+}
+
+nonfree_firmware() {
+	pkgdesc="Modem, WiFi and GPU Firmware, also needed for osk-sdl"
+	depends="firmware-xiaomi-polaris firmware-xiaomi-polaris-initramfs soc-qcom-sdm845-nonfree-firmware"
+	mkdir "$subpkgdir"
+}
+
+phosh() {
+	install_if="$pkgname=$pkgver-r$pkgrel phosh"
+	install -Dm644 "$srcdir"/phoc.ini \
+		"$subpkgdir"/etc/phosh/phoc.ini
+}
+
+sha512sums="
+04077cdb2a6cc541177981209526e9aea6d715f068b59f9176ff1fdf9ba9d0a00aab5b32eeb78cabef4a77dc24cc5b1bbb92385f9471a0bff3cfb0a750aa731c  deviceinfo
+e2e417169345c86a5dd34ac0afac4b2b983a755f4c7ba5698c385a01f96b9bd2c3ace1ce5a0569c121675e8b87e88e1cf5c648e995d9c50cba66e52bbc83753c  phoc.ini
+"