Add en- and disable MMU to M709

[3d-gussner]

Add X42 to erase the MMU eeprom

@gudnimg Any optimization possible?

Related to https://github.com/prusa3d/Prusa-Firmware/issues/4473 and https://github.com/prusa3d/Prusa-Link/issues/872

• [X] Update Doxygen
• [x] Update RepRap wiki
• [x] Update M709 for MK4
  • [X] S0|0 and X0|X1 already implemented
  • [x] Add X42 to erase the MMU eeprom

[github-actions[bot]]

All values in bytes. Δ Delta to base

Target	ΔFlash	ΔSRAM	Used Flash	Used SRAM	Free Flash	Free SRAM
MK3S_MULTILANG	154	0	246116	5634	7836	2558
MK3_MULTILANG	160	0	245410	5643	8542	2549