Add tools to test LXATAC features and speedup bringup.

[lichtfeind]

To speedup bring up of the LXATAC this adds a second binary to collect ADC statistics and test LEDs, display and buttons.

To do this i needed to change the visibility of some structs/types/functions. And add color support.
The color support is probably still flaky as i am unsure how how to check for the color space used by the frame buffer.
It is also still missing color support the the Display view in the web ui.

The ADC part allows to collect ADC samples from multiple channels interleaved. This make measurements hopefully more correlated then the old way of collecting then separately.

The LED,Display ui test display a rainbow on the LCD and cycles the LEDs and LCD backlight when a button is pressed.
After both buttons have registered a press the ui-test will exit. (as this is only tested every ~5 press it might take some addition presses)

[hnez]

Hi,

some high level stuff I have noticed first:

• It was me who suggested building two distinct binaries, but maybe we should rethink that decision, as it leads to a lot of dead code warnings which we would have to work around. How about building one tacd binary instead, that can be the daemon (tacd daemon or plain tacd) and also tacd selftest (or whatever better name we come up with for this feature).

• The change to RGB color on the display is quite invasive for what you want to achieve (displaying color in selfest mode) and I am not too stoked about changing the framebuffer handling, because it has broken before due to changes on what the framebuffer emulation in the kernel has given us. Could'nt you get away with just writing to the Framebuffer struct directly in the selftest mode to display color?

    display.with_lock(|target| {
        // Do something with `target.0.frame`
    });

• I would prefer the last commit to be split up into smaller changes for better reviewability.

[hnez]

We are quickly getting there. Please have a look at some of the remaining comments I had, feel free to dismiss some of them as nitpicking, if you think so, and rebase the changes into a clean format that we can merge.