Fix CHEETAH v2.0 Bltouch bug

[GerogeFu]

The default PROBE pin(PA0) cannot used as OUTPUT pin as it has BAT85. To solve this problem, we need to use Z-MIN(PB1) pin for SERVO PWM output and use PROBE pin for Z_STOP. And PB1 corresponding timer is TIMER3

[thinkyhead]

This is confusing. The Probe pin is never an output, always an input. Only the servo pin that sends commands to the BLTouch needs to be an output. If we're looking for a way that you could have both a Z endstop (used for homing) and a BLTouch probe (not used for homing), it looks like that wouldn't be possible. But, it would be possible to have both a PROBE pin and a Z-STOP pin for simple probes that don't need a Servo / PWM pin to receive commands. I'll try to make that more explicit here and see how it fares.

[thinkyhead]

From other sources, it does appear that PA0 is the sensor pin and PB1 is the "BLTouch/PWM" Servo (control) pin.

Just make sure to set Z_MIN_PROBE_USES_Z_MIN_ENDSTOP_PIN for BLTouch (and other probes) for the best results, otherwise Marlin will assume there is a separate Z endstop and the servo pin (PB1) will be chosen as the (default) Z probe signal pin.