This fixes/improves a few issues with I2C support:
* Validate I2C pins, so only pins that are supported by the hardware
can be used (similar to how it's done with PWM).
* Add address to Tx API (without it, the simulator can't really
simulate I2C).
* Add frequency when configuring. Not currently used, but might be
useful in the future and adding it now avoids possibly breaking
changes.
This is a breaking change, but since the simulator doesn't support I2C
yet that seems fine to me. (It does in my local changes, but those need
to be cleaned up before I can push them).
I only discovered this issue after a while. All the baremetal PWM
implementations use pointers to a PWM instance, instead of the PWM
instance itself. For consistency (and because it's a better idea in
general), the simulated PWMs need to work the same.
Ayke van Laethem