testing/device-oneplus-oneplus3t: add gpu acceleration support

This MR adds GPU acceleration support for Oneplus 3T. Includes fixes for known issues from xiaomi-scorpio.

Tested with phosh for a few hours and ran glxgears (145fps). Needs additional suspend fix/workaround (https://gitlab.com/pmos-oneplus3t/linux/-/wikis/oneplus3t-mainline-suspend-fix). After suspend fix the screen stays on and phosh is usable.

Known issue: pressing power button switches the screen off and screen does not turn back on when pressing power button again. I will work on properly fixing the suspend issue and make power button/backlight control work and submit separate patches.