samples: blinky: add support for non-standard led displays

[AndOrangutan]

This is a change to enable the blinky sample to work on matrix displays such as the common learner board MicroBit v2.

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[sambhurst]

Hello @AndOrangutan, thanks for extending the blinky sample code so that it works on boards without a simple LED connection. Could you updated the README.rst to include the additional LED and how the two LED pins work together to toggle a single matrix LED. And that the additional LED is optional for non-matrix LED displays, but if it's implemented, blinky will simply toggle both LEDs.

[kartben]

This is complexifying blinky quite a bit for a sample that's meant to be pretty much the next step after "hello world" for most users. I might be missing somethign but it looks like what's needed is rather a new binding/driver that would allow to configure a given LED from an LED matrix as an LED device?

[AndOrangutan]

True, @kartben, technically the root problem I wanted to solve was there being no working blinky example for the MicroBit v2 board. I'm not really sure how many other boards even have matrix displays, but I see a couple ways of remedying it:

1. Creating a board specific example for the MicroBit v2.
2. Creating a more general binding/driver.
3. Something like my solution.

With this board being a learner board, it would be useful to have some sort of working blinky. I'm not trying to add unneeded complexity, do you have a preferred solution?

[sambhurst]

Hello @kartben, could you comment on @AndOrangutan reply?

[kartben]

True, @kartben, technically the root problem I wanted to solve was there being no working blinky example for the MicroBit v2 board. I'm not really sure how many other boards even have matrix displays, but I see a couple ways of remedying it:

1. Creating a board specific example for the MicroBit v2.
2. Creating a more general binding/driver.
3. Something like my solution.

With this board being a learner board, it would be useful to have some sort of working blinky. I'm not trying to add unneeded complexity, do you have a preferred solution?

Ya I think solution 1 is probably better (although note that there is already a sample for the LED matrix).
Your suggested solution is really making blinky too "bloated" (for the lack of a better word, sorry) to most users. And even the led0 / led1 are confusing are they're not corresponding to actual LED "pins".
solution number 2 might be interesting to explore if we think there is value in proposing a generic binding for describing a group of GPIOs meant to be manipulated as one single "virtual" GPIO, I guess?