tested:
* board.LED
* neopixel as status LED
* i2c scan finds lis3dh sensor
* psram capacity
not tested:
* rgb matrix o_O
* the gpio pins
Introduce new `board` properties for matrixportal-style boards:
* MTX_COMMON
* MTX_ADDRESS
These are intended to simplify use of the RGBMatrix constructor:
```py
matrix = RGBMatrix(..., addr_pins=MTX_ADDRESS[:3], **MTX_COMMON)
```
removing the need for sending in the following individual parameters:
* rgb_pins
* clock_pin
* latch_pin
* output_enable_pins
and making construction of a 16/32/64-row display easy by slicing a tuple
of all address pins rather than writing out the individual pins. If it
works out it'll be ported back to the matrixportal m4 as well.
Jeff Epler