Add predefined AUTO_FAN_PINs to pins files

[thinkyhead]

…well, some pins files.

As suggested by #5011 (comment)

• Fix broken _GET_TIMER macro in fastio.h
• To ease transition, rename EXTRUDER_n_AUTO_FAN_PIN to En_AUTO_FAN_PIN
• Sanity check for the old setting
• Add ORIG_En_AUTO_FAN_PIN for use by pins files as the suggested auto fan pins
• Update commentary for the auto pins options in Configuration_adv.h
• Sanity check: If the fan speed is under 255 the selected pins must be PWM-able
• Supply default auto fan pins for some boards — based on example configurations
• Use EXTRUDER_AUTO_FAN_SPEED only for PWM-able pins, else use 255
• Constrain auto fan pins, limited by HOTENDS
• For Cartesio fix some issues: Allow a single status LED. Allow keypad with CartesioUI.