Update Marlin G-code summary

Marlin/src/gcode/gcode.h

  * M34  - Set SD Card sorting options. (Requires SDCARD_SORT_ALPHA)
  * M42  - Change pin status via gcode: M42 P<pin> S<value>. LED pin assumed if P is omitted.
  * M43  - Display pin status, watch pins for changes, watch endstops & toggle LED, Z servo probe test, toggle pins
- * M48  - Measure Z Probe repeatability: M48 P<points> X<pos> Y<pos> V<level> E<engage> L<legs> <S>chizoid. (Requires Z_MIN_PROBE_REPEATABILITY_TEST)
+ * M48  - Measure Z Probe repeatability: M48 P<points> X<pos> Y<pos> V<level> E<engage> L<legs> S<chizoid>. (Requires Z_MIN_PROBE_REPEATABILITY_TEST)
  * M75  - Start the print job timer.
  * M76  - Pause the print job timer.
  * M77  - Stop the print job timer.
  * M868 - Report or set position encoder module error correction threshold.
  * M869 - Report position encoder module error.
  * M900 - Get or Set Linear Advance K-factor. (Requires LIN_ADVANCE)
- * M906 - Set or get motor current in milliamps using axis codes X, Y, Z, E. Report values if no axis codes given. (Requires HAVE_TMC2130)
+ * M906 - Set or get motor current in milliamps using axis codes X, Y, Z, E. Report values if no axis codes given. (Requires HAVE_TMC2130 or HAVE_TMC2208)
  * M907 - Set digital trimpot motor current using axis codes. (Requires a board with digital trimpots)
  * M908 - Control digital trimpot directly. (Requires DAC_STEPPER_CURRENT or DIGIPOTSS_PIN)
  * M909 - Print digipot/DAC current value. (Requires DAC_STEPPER_CURRENT)