[2.0.x] Fix switching extruder

`DONT_SWITCH` got lost along the way. Replace it with `DO_SWITCH_EXTRUDER` and adjust the code.

[2.0.x] Add FAN_MAX_PWM

[2.0.x] Prevent compilation of unused u8g-oriented code

Fix #10699

Fix #10708

As pointed out in #10731

[2.0.x] Smarter MIN, MAX, ABS macros

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>

Co-Authored-By: Zwaubel