Twrp device tree for the Retroid Pocket 2

Based on https://github.com/mt8163/android_device_bq_aquaris_m8 and https://github.com/Black-Seraph/android_twrp_gpd_gpd_en

Thanks to @R0rt1z2 & @488315 for helping on this! Special thanks to Retroid for releasing kernel source code! Thanks to @thoramund(github.com/thoramund) for tweaking the 320x240 theme to work with Retroid Pocket 2