(so 0 to 255 now goes from 0.00V to 5.10V)

For 3V LEDs on a boost/buck dual fuel driver, this allows
routing power around the boost converter in li-ion mode,
to reduce resistance and increase maximum output.
The AA/NiMH mode is unaffected, and boosts as normal.

This helps when using a regulator which doesn't like being turned off
and back on quickly.

- fixed t1616 Vref values getting clobbered sometimes,
  wrapped setting those in a #define'd function for ease and consistency
- moved some DAC definitions from hw/ to arch/ to reduce repetition
- fixed thefreeman's other builds
- switched from PWM_TOPS to PWM2_LEVELS (I'm trying to phase out _TOPS)

(realtime voltage colors, and no simple UI by default)

Before this branch, `voltage` was 6 bits: Volts * 10
A couple patches ago, I upgraded it to 16 bits: 65535 * Volts / 10.24
That costs too much extra ROM on attiny85 though, for extra precision
it doesn't even use... so I switched back to an 8-bit value.  It's still
more precise than before though: Volts * 40
... and battcheck displays an extra digit now, on devices with ROM for it.
... and battcheck waits a second to get a more accurate measurement
    before displaying the first value.  It has *much* less variation
    between first and later readings now.

Also:
- got t1616 builds working again (tested fc13 and thefreeman-boost-fwaa)
- upgraded t1616 voltage and temp to 12-bit (10 bits + 4x oversampling)
- removed expensive temp conversion from t1616 ADC interrupt
- recalibrated t1616 bogomips again; runs faster after interrupt fix
- increased t1616 internal VDD measurement resolution by 36% (1.5V Vref, not 1.1V)
- fixed sloppy setting of Vref bits

I still need to test / update other t1616 builds,
and fix all the t85 + t1634 code and build targets.

This patch changes the ADC code to use two internal standard units, and
everything else must convert to these units:

- FSM Volts: centiVolts << 6  (range 0 to 10.24 V per cell)
- FSM Kelvin: Kelvin << 6  (range 0 to 1024 K)

UI-level voltage is still "Volts * 10", and temperature is still Celsius.

FSM expects functions to be provided, to convert from the hardware's
raw ADC measurements to these internal units:  `voltage_raw2cooked()`
and `temp_raw2cooked()`.  Defaults will be provided by arch/*.[ch] for
each MCU type, or the hwdef can make its own.

Anyway, gotta go fix all the other MCUs and builds now.  :(

ADC doesn't work yet.  No voltage, no temperature.
I need to do a lot of refactoring on the ADC code.  :(