Removed the combined .dtsi file for each group of common layouts, and
split the position map across the files in each group. This makes
reading the position maps slightly more difficult, but it aligns the
common layouts with the keyboard-specific ones such as
foostan/corne.dtsi in that simply including each header adds the
layout, with no need to set status = "okay".
* Add Corne and Ferris shared layouts, and update the respective
shields to use them.
* Add a sample Hummingbird physical layout for testing posix xiao.
* Add Sofle physical layout as an additional reference.
