Better screen drivers? Waveshare 3.5" ili9486 TFT is choppy

In general, [the driver Waveshare recommends for their TFT '(A)' model display](https://www.waveshare.com/wiki/3.5inch_RPi_LCD_%28A%29) is wonky.

Their install script overwrites `config.txt`, and the driver isn't a DRM driver, so the screen seems to refresh very slowly, like 5 fps. And the SPI driver also seems to eat up CPU cycles, which is annoying.

And because it's not DRM, you have to use `--qt-preview` or use the QT software renderer to get camera output to screen. So that's really choppy too, and also induces more CPU load!

There's a `waveshare,rpi-lcd-35` driver in https://github.com/raspberrypi/linux/blob/rpi-5.15.y/drivers/gpu/drm/tiny/ili9486.c, but there's no overlay available for it... would be nice to have a high-refresh touchscreen instead of the laggy one here...

Start by reviewing the Waveshare install script and its config.txt changes, then compare them with the Raspberry Pi Linux DRM driver at drivers/gpu/drm/tiny/ili9486.c. Determine what overlay support would be needed for this display. Done means providing a workable high-refresh touchscreen setup without the reported choppy rendering and excessive CPU load.

Written by the indexing model from the issue text.