Co-Authored-By: borsegbr <borsegbr@users.noreply.github.com>

Allow `ENABLED`, `DISABLED`, `PIN_EXISTS`, and `BUTTON_EXISTS` to take multiple arguments. Also add:
- Alias `ANY(...)` for `!DISABLED(...)`
- Alias `ANY_PIN(...)` for `PIN_EXISTS(a) || PIN_EXISTS(b) ...`
- Alias `EITHER(A,B)` for `ANY(...)`
- Alias `ALL(...)` and `BOTH(A,B)` for `ENABLED(...)`
- `NONE(...)` for `DISABLED(...)`

See https://github.com/pinchies/Marlin/pull/1#issuecomment-471388743

* Apply #pragma once in headers
* Adjust some thermistors formatting
* Misc cleanup and formatting

…as with #10540

Co-Authored-By: per1234 <per1234@users.noreply.github.com>

* AVR: Atomic bit set and clear

The critical section can be dropped, saving 3 cycles per access. Also simplified pin toggling for all ports.

This is an initial cut for feedback, updated for 2.0.x.

Chamber temperature is currently reported along with hot end and bed
temperatures to serial. The format is just like that used for hot end
and bed temperatures, but using 'C' prefix. As there is no heater,
target is always 0. Is this appropriate, is there a better way to report
chamber temperatures?

Chamber temperatures are not reported on the LCD in any way.

When auto chamber fan is enabled, it currently just uses the same
temperature threshold as the other auto controlled fans.

As the chamber temperature is not connected to any heater, it doesn't
undergo mintemp/maxtemp monitoring. This would need to change in the
future if chamber heating became a feature.

Implement AVR Platform

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Configuration_adv.h changes

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add "live" LCD update

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P & S version

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final (hopefully) tested version

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update M115 capabilities print

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Menu changes portion of the requested changes

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changed USEABLE_HARDWARE_PWM from a function to a series of macros

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changes per review

Replace all fastDigitalRead/Write() with READ/WRITE()

Define SCK_PIN, MISO_PIN, MOSI_PIN in pins.h if not already defined in the pins_*.h files.

Remove these conditional pin definitions from the pin-files. They are now always defined.

Define separate sets of SPI-pins for AT90USB with and without Teensy support in fastio.h.
Likely this was the main reason for all that confusion about the AT90USB-SPI pins.