drivers: sensor: tenstorrent: pvt: refactor driver

[alexapostolu]

Refactor the PVT driver. There's been some CI failures where temperature readings have been outside the [40, 70] range.

The readings beyond 70 are no more than 71, so we increase the max to 75.

The readings below 40 hover near 0. I can't reproduce it, but I suspect this might be a data conversion issue. I refactored the PVT driver to have less data conversions, to use q31_t instead of float, and just basic refactoring to make the code simpler.

[alexapostolu]

@afongTT Just confirming, is 75 a reasonable max limit for the temperature test? There's at least two CI runs now that have the chip temperature at 71 C

[cfriedt]

I've seen a bunch of tests where it's failing at close to zero degrees (at least according to logs), so well outside of the [40,70] range.

In this case, it's on yyz-zephyr-02 so is in the Toronto 11th floor lab. To me, it does not make any sense why we would be reading close to 0 degrees C.

https://github.com/tenstorrent/tt-zephyr-platforms/actions/runs/19913215921/job/57086440153

[alexapostolu]

@cfriedt I'll take another look at the PVT driver to see if there's a bug in the implementation

[cfriedt]

@alexapostolu - are we is not floating point in Pvt?

[alexapostolu]

@cfriedt We're not using the float type directly but we are still representing the decimal place using struct sensor_value.

[afongTT]

@afongTT Just confirming, is 75 a reasonable max limit for the temperature test? There's at least two CI runs now that have the chip temperature at 71 C

Yeah, I think increasing the max to 75 or 80 would be reasonable. But the 0 degree reading isn't right.

[alexapostolu]

I don't think this PR can be merged anytime soon. To merge it, then we either have to add functions just for converting between raw sensor value to telemetry value and vice versa (which would be redundant), or change the arc message format (with won't be until the next major version upgrade).