See #11097

As noted in #10965

- Ordering and match classification between `boards.h` and `pins.h`
- Check `pins.h` environments

Co-Authored-By: ejtagle <ejtagle@hotmail.com>

Co-Authored-By: Simon Swenson <simon-swenson-8351@users.noreply.github.com>

Based on #10519

Co-Authored-By: Alex <alex18881@users.noreply.github.com>

What should the SD detect and SDSS pins be? Followup soon on #8138

* Add BOARD_MKS_BASE_15 with digital micro-stepping
* Rename MKS_13 to MKS_GEN_13

This is an initial cut for feedback, updated for 2.0.x.

Chamber temperature is currently reported along with hot end and bed
temperatures to serial. The format is just like that used for hot end
and bed temperatures, but using 'C' prefix. As there is no heater,
target is always 0. Is this appropriate, is there a better way to report
chamber temperatures?

Chamber temperatures are not reported on the LCD in any way.

When auto chamber fan is enabled, it currently just uses the same
temperature threshold as the other auto controlled fans.

As the chamber temperature is not connected to any heater, it doesn't
undergo mintemp/maxtemp monitoring. This would need to change in the
future if chamber heating became a feature.

http://reprap.org/wiki/EinsyRetro

- Assign 243 (like EFB) as Ender-4/CR-8 board ID
- Add to `Makefile`
- Add to `pins.h`

Followup to 436e5b7