arm64: dts: qcom: Add Xiaomi Libra (Mi 4C) device tree

This commit adds support for the Xiaomi Libra (Mi 4C)
smartphone. It's based on the Qualcomm msm8992 SoC.

It currently supports:
* Screen console from bootloader
* SDHCI
* Regulator configuration
* Serial console
* I2C

Signed-off-by: Konrad Dybcio <konradybcio@gmail.com>
Link: https://lore.kernel.org/r/20200625182118.131476-13-konradybcio@gmail.com
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>