- Also implemented real endstop reading on interrupt.

Disabling an ISR on ARM has 3 instructions of latency. A Memory barrier is REQUIRED to ensure proper and predictable disabling. Memory barriers are expensive, so avoid disabling if already disabled (See https://mcuoneclipse.com/2015/10/16/nvic-disabling-interrupts-on-arm-cortex-m-and-the-need-for-a-memory-barrier-instruction/)

Co-Authored-By: ejtagle <ejtagle@hotmail.com>

Co-Authored-By: ejtagle <ejtagle@hotmail.com>

Use macros that explicitly avoid double-evaluation and can be used for any datatype, replacing `min`, `max`, `abs`, `fabs`, `labs`, and `FABS`.

Co-Authored-By: ejtagle <ejtagle@hotmail.com>

- Cleanups, fixes for Due HAL code.
- TC_IER is write-only. Use TC_IMR to test ISR state.

Co-Authored-By: ejtagle <ejtagle@hotmail.com>

…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.

Also simplify logic on all ARM-based interrupts. Now, it is REQUIRED to properly configure interrupt priority. USART should have highest priority, followed by Stepper, and then all others.

Responding to https://github.com/MarlinFirmware/Marlin/pull/8833#issuecomment-379426803

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.

- And implement the `backtrace()` function call

The `_O2` attribute is no longer needed on the malyanlcd function, and the macros have broken timer numbers - reset this to a function to return the right device. Also fix the bit order cast in SPI.