arm64: dts: qcom: msm8916: Add device tree for Huawei Ascend G7

arm64: dts: qcom: msm8916: Add device tree for Huawei Ascend G7

The Huawei Ascend G7 is a smartphone from Huawei based on MSM8916.
It's fairly similar to the other MSM8916 devices, the only notable
exception are the "cd-gpios" for detecting if a SD card was inserted:
It looks like Huawei forgot to re-route this to gpio38, so the correct
GPIO seems to be gpio56 on this device.

Note: The original firmware from Huawei can only boot 32-bit kernels.
To boot arm64 kernels it is necessary to flash 64-bit TZ/HYP firmware
with EDL, e.g. taken from the DragonBoard 410c. This works because Huawei
forgot to set up (firmware) secure boot for some reason.

Also note that Huawei no longer provides bootloader unlock codes.
This can be bypassed by patching the bootloader from a custom HYP firmware,
making it think the bootloader is unlocked. I use a modified version of
qhypstub [1], that patches a single instruction in the Huawei bootloader.

The device tree contains initial support for the Huawei Ascend G7 with:
  - UART (untested, probably available via some test points)
  - eMMC/SD card
  - Buttons
  - Notification LED (combination of 3 GPIO LEDs)
  - Vibrator
  - WiFi/Bluetooth (WCNSS)
  - USB

[1]: https://github.com/msm8916-mainline/qhypstub

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20210514104328.18756-1-stephan@gerhold.net
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>