This commit gives the option to not pass an I2C Bus ID when creating a
machine I2C object. If the ID is not provided, the default bus ID (which
is `PICO_DEFAULT_I2C`) is used.
This allows users to simply declare an I2C object with `machine.I2C()`
without passing any arguments, thus creating an object with the default I2C
ID, SCL, and SDA.
Signed-off-by: Malcolm McKellips <malcolm.mckellips@sparkfun.com>
bb4ec886f8