* Relocate platform specific drivers

* Move stm eeprom

* Tidy up slightly

* Extensible split data sync capability through transactions.

- Split common transport has been split up between the transport layer
  and data layer.
- Split "transactions" model used, with convergence between I2C and
  serial data definitions.
- Slave matrix "generation count" is used to determine if the full slave
  matrix needs to be retrieved.
- Encoders get the same "generation count" treatment.
- All other blocks of data are synchronised when a change is detected.
- All transmissions have a globally-configurable deadline before a
  transmission is forced (`FORCED_SYNC_THROTTLE_MS`, default 100ms).
- Added atomicity for all core-synced data, preventing partial updates
- Added retries to AVR i2c_master's i2c_start, to minimise the number of
  failed transactions when interrupts are disabled on the slave due to
  atomicity checks.
- Some keyboards have had slight modifications made in order to ensure
  that they still build due to firmware size restrictions.

* Fixup LED_MATRIX compile.

* Parameterise ERROR_DISCONNECT_COUNT.

* ws2812: Fix number of nops for AVR at 8 MHz

When trying to calculate the number of nops for AVR running at 8 MHz,
the value of `w3` is expected to be negative; however, because `F_CPU`
is defined in tmk_core/avr.mk with the `UL` suffix, the preprocessor
performs its calculations using `unsigned long`, getting a very large
positive number instead of the expected negative number; this then
results in generating code with a huge number of nops.  Fix the broken
calculations by performing a comparison before subtraction, so that the
unsigned number wraparound does not occur.

The keyboard which triggers the problem is `handwired/promethium`; the
buggy code silently compiles, but the resulting timings would be
completely wrong.

* ws2812: Clean up the code after the 8 MHz fix

Remove old code which was unsuccessfully trying to clamp negative w1, w2
and w3 values to 0, and set w1_nops, w2_nops and w3_nops directly.

* at90usb162 support

* fix missing bracket

* Apply suggestions from code review

Co-authored-by: Ryan <fauxpark@gmail.com>

Co-authored-by: Ryan <fauxpark@gmail.com>

* Rewrite APA102 support

The APA102 source was broken by commit 16a15c1cfcbfd0feb2c2cf1383676747e2f97d73 as it did not include the
quantum header. This commit addresses that, as well as other issues with
transferring bytes over the SPI interface, i.e. it was not setting the
clock pin back to low after sending a bit.

The deviation when sending the end frame is kept, but updated to the
latest from the referenced project.

Finally, these changes expose the global LED brightness parameter
of the APA102. Brightness values are configurable through
`APA102_DEFAULT_BRIGHTNESS` and `APA102_MAX_BRIGHTNESS`.

* Fix typo in led brightness extern

* Move driver out of AVR directory and add delay for ARM

* Experimental APA102 support on AVR and ARM

Co-authored-by: Alde Rojas <hello@alde.io>

* Refactor apa102_send_byte() calls to a loop

* Implement io_wait function for ARM

* Move APA102 drivers to own directory, fix copyright notice

* Add APA102 keymap to handwired/onekey

* Simplify RGBLIGHT_ENABLE/DRIVER option handling

Co-authored-by: Mikkel Jeppesen <2756925+Duckle29@users.noreply.github.com>