Support setting microsteps via GCODE on TMC stepper drivers

[repvik]

Description

Marlin supports setting microsteps using M350 GCODE. This code depends on there being two GPIO pins to control the microstepping. The TMC driver supports microstepping, but does not change stepping when M350 is issued.

This will allow one to replace steppers and change microstepping without recompiling firmware.

[matthew-humphrey]

I researched this a bit, and here is what I found:

The current implementation of the M350 command only works with stepper drivers whose microstep ratio is controlled via GPIO. For TMC2130, the microstep ratio is controlled via SPI. It is initialized by a call to reset_stepper_drivers() which in turn calls tmc2130_init_to_defaults, which in turn calls tmc2130_init (via a macro, _TMC2130_INIT). The macro passes a #define for the appropriate axis, for example X_MICROSTEPS. These are defined in Configuration_adv.h.

reset_stepper_drivers() is called in M502 (reset configuration). So in theory it could be added by using EEPROM to store setting, and then using this value instead of hard-coded value