lg-madai: new device (LG Fx0)

This time I am bringing a Firefox OS device.

Although Fx0 uses MSM8926, and there is a LineageOS kernel for LG MSM8926 devices, I used vendor kernel because the display panel and touch drivers are missing in the LineageOS kernel. Also I am still questioning whether contributing to just the kernel part of LineageOS makes sense, as I am not willing to port a complete LineageOS or Android on this device. As seen on https://github.com/peremen/android-kernel-lg-madai/commits/main LG forgot to run make mrproper on their vendor kernel, and excluded the prima Wi-Fi driver, I had to borrow that part from LineageOS kernel but the firmware situation is a bit complicated (WCNSS_cfg.dat from Qualcomm, WCNSS_qcom_cfg.ini and WCNSS_qcom_wlan_nv.bin scattered in different parts of the device). Patches also affecting Android/FxOS compilation is directly included in the kernel fork repository, and patches only relevant to postmarketOS are included here.

According to the service manual there is a UART exposed through debug connector, but it is not populated by default. That might be required for any further kernel development.

Anyway, Xfce desktop works, but I couldn't see the shutdown menu on Xfce4 (have to manually do that using terminal).