This change adds a common I2C class, gathering various I2C functions into a single point of responsibility.
It's necessary for correctly managing the I2C bus pins and state across multiple devices.
* Add a common/pimoroni.hpp to list default pins for various add-ons
* Move the BG SPI Slot enum here for safe keeping
* Switch all GPIO pin references to "uint" to match Pico SDK and bring back PIN_UNUSED as UINT_MAX
Confused myself by plugging this into a BG base. It gave all the appearance of working, but the time was not counting up.
Turns out the library will happily talk to no device whatsoever and when you "set_time" it's stored in an C array and returned as if it came from the RTC.
Phil Howard
ZodiusInfuser
Simon Reap