For split keyboards using an IO expander over TRRS/i2c, if the
right half isn't connected, we should be able to gracefully
fallback to the left side still working.

Refactored the GPIO matrix kscan driver so that only the data and config
structures are defined in the foreach macro. Functionality is unchanged
except for the addition of DT properties to adjust polling speed.

This should make it easier to add other enhancements later, like
improved and customizable debounce behavior.

* Move to `DEVICE_DT_INST_DEFINE` everywhere.

See: https://docs.zephyrproject.org/2.5.0/releases/release-notes-2.5.html#deprecated-in-this-release
PR: https://github.com/zmkfirmware/zmk/pull/736

+ Add a 1us sleep to let the column selection settle in order to avoid spurious keypresses when row capacitance is high (like on the encoder row)

* Add easier macros for conditional polling/interrupt code.
* Properly continue polling on intervals, without extra
  enable/disable code for pins that is superfluous when not trying to
  deal with interupts firing.
* Fix to allow multiple GPIO drivers when doing splits w/ IO expanders

* Actually allow defaulting yes in other places.

Aligns *.h and *.c to underscore naming convention.

These were kept (with warnings) for backwards compatibility with external boards/shields:
- kscan-mock.h
- matrix-transform.h
They should be removed in the future.

PR: #523

Replaced with RegExp: /(?<!const )(struct device \*)/g

See: https://docs.zephyrproject.org/latest/releases/release-notes-2.4.html
PR: #467