Perform most arithmetic with scaled integer values.
For my calibration values
```
const uint32_t NVMCTRL_TEMP_LOG[]={0xfc05511e, 0xcc7ac0f7};
```
the maximum difference between the old and new calculation is 0.50°C.
The difference is smallest (0.13°) at 25.87°C in the old scale.
This reduces mcu_processor_get_temperature from 568 bytes to 348 bytes
(-220 bytes)
b251e78ac5