RFC: Split device-specific code to different files

[fenugrec]

Draft, still thinking about this. Comments welcome.

Since we don't have tons of device-specific code yet, I was putting all the code into a single file per mcu type. This may become impractical if

• mcus from a same family have different CAN/USB peripherals , or more fundamental differences
• adding tons of unrelated functions like what I've started here, with CAN and system clock config in the same file, may become messy. But maybe still manageable : only bits left are GPIO and USB.

GPIO may end up in a board-specific hierarchy instead, still thinking about this.

[marckleinebudde]

Haven't tested but looks good!