Marlin 2.0.7.2 release for Anycubic Mega Zero (Unified)

This is pre-release of unified config.
One code base with multiple PlatformIO build targets should be able to produce working firmware builds for Anycubic Mega Zero.

Build variants:

• Anycubic Mega Zero stock board
  • Simple configuration
  • Manual Mesh Bed Leveling
  • Automatic bed leveling using BLTouch. BLTouch servo signal uses pin 27. BLTouch probe signal can be put either to EXT-A2 or to ZMIN endstop
• SKR mini MZ V1.0 or BTT SKR mini E3 V2.0
  • Simple configuration includes manual mesh bed leveling
  • Heated bed configurations
  • Automatic bed leveling using BLTouch. BLTouch servo signal uses designated connector. BLTouch probe signal can be put either to designated connector or to ZMIN
  • NeoPixel support is enabled
  • Experimental builds with nanolib: this reduces flash size requirements and allows to enable more features, but can contain compiler bugs.

Flashing:

• Anycubic Mega Zero stock board
  • From source:
    • Validate that it builds: pio run -e anycubic_mega_zero_xxx
    • Flash it: pio run -e anycubic_mega_zero_xxx -t upload
  • Octoprint Firmware Flasher: use corresponding to your needs HEX file, e.g. anycubic_mega_zero_mbl-firmware.hex
  • CLI, avrdude:
    avrdude -v -p atmega1284p -c arduino -b 115200 -D -P /dev/ttyUSB0 -U flash:w:anycubic_mega_zero_mbl-firmware.hex:i
• BTT SKR mini E3 V2.0 or SKR mini MZ V1.0
  • Binary: download to microSD card from release page according to your needed feature set. Example: anycubic_mega_zero_btt_bed_bl_zmin-firmware.bin
  • Build your own binary from source:
    • pio run -e anycubic_mega_zero_btt_xxx
    • then put resulted binary .pio/build/anycubic_mega_zero_btt_xxx/anycubic_mega_zero_btt_xxx-firmware.bin to microSD card
  • rename file on microSD card to firmware.bin
  • power cycle your printer with microSD card inserted. Firmware will be updated and printer will reboot.