i2c: switch all i2c drivers definitions to use i2c bus interface type

[deadprogram]

This PR switches all i2c drivers definitions to use i2c bus interface type instead of machine package concrete type.

Once it is merged into dev, then individual drivers can have tests added as time permits.

[deadprogram]

I am working in branch https://github.com/tinygo-org/drivers/tree/adt7410-tests-improvements on improvements to the ADT7410 based on this branch.

[aykevl]

I checked code size differences using make smoke-test and there are indeed some differences. Often in the 20-100 byte range, but sometimes larger. The largest I've seen was somewhere in the 500 byte range (although there is also a decrease).

I think this is worth the cost, especially considering the testability improvements and increased flexibility. Interfaces will allow the use of software I2C for any driver, which may come in use when you don't get to choose pins or existing I2C pins cannot be used.

[deadprogram]

Thanks for the review, now merging.

[conejoninja]

Now that this has been merged, should we do something similar with SPI? That would be helpful with issue #151 were a driver implements both I²C and SPI, but the board only implements one of those and fails to compile.

[deadprogram]

Yes, that is for sure the next step.