Modify pin assignments to improve breakout board layout

[dihm]

The current pin assignments were mostly chosen before the board layout was made, resulting in a breakout board that has a large number of long, winding traces. I'm pretty sure we could choose better pin assignments that would make the board layout much better.

[dihm]

I've had a first go at a better design, and I'm reasonably sure the following layout and pin assignments are valid.

#define PIN_MISO 0
#define PIN_MOSI 19
#define PIN_SCK 4
#define PIN_SYNC 1
#define PIN_CLOCK 21
#define PIN_UPDATE 6
#define PIN_RESET 2
#define P0 10
#define P1 9
#define P2 8
#define P3 7
#define TRIGGER 16

Pretty confident the only pins that are restricted are the SPI pins (MOSI, MISO, SCK) and the Clock output, which this respects. A number of minor code changes beyond updating the pin assigments are required.

• Switch to SPI0 instead of SPI1
• Ensure the pio code defines the profile pins correct (right now it takes a reference pin and counts up, it needs to count down now)
• Probably a few other places

I'm milling a test board now to ensure functionality with the pin changes. @carterturn If not too disruptive to your efforts, I plan to put together a PR with minimum number of changes required for things to nominally function.