More logic and convenience for BTT SKR Pro

[MarkusThur]

Requirements

The BTT SKR Pro Board opens a lot of options for the user. Unlike for other BTT boards the pin header is file is very "simple"

Description

This pull requests adds some more logic to the file to automatically assign pins if user enables options:
Y_DUAL_STPPER_DRIVERS
NUM_Z_STEPPER_DRIVERS > 1
TEMP_SENSOR_PROBE
TEMP_SENSOR_CHAMBER
USE_CONTROLLER_FAN
It tries to identify unused pins for those options and assigns them if possible without need for the user to modify this file

Furthermore if Sensortypes -4 or 20 (which do not need a pullup resistor / are incompatible with pullup Resistors) are selected for a specific sensor the pin gets reasigned to pullup free ADC Pins of Extension1.

Benefits

Reduces the need to modify this file if named options are activated. More nice options can be added.

Configurations

Related Issues

[thinkyhead]

The pins_postprocess.h file automatically handles assigning X2, Y2, Z2, etc. to the unused E steppers based on settings, and the aim is to make the pins / boards as separate as possible from the machines they ship with so that you can use any board in any machine with any axis setup you need.

[thinkyhead]

Note that GitHub has a bug where we cannot make changes through git or GitHub Desktop on forks that are not directly cloned from MarlinFirmware/Marlin. So, I'm closing this PR and creating a new one from my own fork in order to continue to making changes. I will link the new PR shortly.