Do it all at once in preparation for Go 1.18 support.
To make this commit, I've simply modified the `fmt-check` Makefile
target to rewrite files instead of listing the differences. So this is a
fully mechanical change, it should not have introduced any errors.
This commit changes the I2C declarations so that the objects are
instantiated in each chip file (e.g. machine_atsamd21e18.go) and used to
define I2C0 (and similar) in the board file (e.g. board_qtpy.go). This
should make it easier to define new board files, and reduces the need
for separate *_baremetal.go files.
I have tested this the following way:
- With the LIS3DH driver example on the Circuit Playground Express and
the PyBadge.
- With the LSM6DS3 driver example on the Arduino Nano 33 IoT.
They both still work fine.
