Co-authored-by: espr14 <espr14@users.noreply.github.com>

* Add a separate GTR board/variant.
* Revert SKR Pro MOSI (before 248b7dfa).

Fixes #17940

Fixes #17955

Co-authored-by: Scott Lahteine <github@thinkyhead.com>

See #17323

This makes babystepping more reliable and may improve Trinamic motion overall.

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

Fixes #17870

Co-Authored-By: Matthew Kennedy <mattkenn4545@gmail.com>

Fixes #17348