lenovo-a8-50f: new device

Oreeeeerequested to merge
Oreeeee/pmaports:lenovo-a8-50f into master

Wiki page: https://wiki.postmarketos.org/wiki/Lenovo_TAB_2_A8-50F_(lenovo-a8-50f)

Splash works, boots to Xfce4, touch works.

A patch was included to fix a kernel panic when interacting with audio devices and these are detected correctly now, but audio doesn't play due to missing memfd_create syscall in 3.10.

I couldn't get WiFi to work which makes the firmware package kind of useless, but I'm leaving it for completeness and maybe for getting this to work on a mainline kernel in the future.

Kernel config passes the kconfig check.

This device's fastboot has issues when flashing rootfs and it doesn't work with mtkclient, so adb sideloading through TWRP is currently the best way to flash postmarketOS.

Merge request reports